The history of science covers the development of science from ancient times to the present. It encompasses all three major branches of science: natural, social, and formal. Protoscience, early sciences, and natural philosophies such as alchemy and astrology that existed during the Bronze Age, Iron Age, classical antiquity and the Middle Ages, declined after the emergence of modern sciences during the Scientific Revolution.
The earliest roots of scientific thinking and practice can be traced to Ancient Egypt and Mesopotamia during the 3rd and 2nd millennia BCE. These civilizations' contributions to mathematics, astronomy, and medicine influenced later Greek natural philosophy of classical antiquity, wherein formal attempts were made to provide explanations of events in the physical world based on natural causes. After the fall of the Western Roman Empire, knowledge of Greek conceptions of the world deteriorated in Latin-speaking Western Europe during the early centuries (400 to 1000 CE) of the Middle Ages, but continued to thrive in the Greek-speaking Byzantine Empire. Aided by translations of Greek texts, the Hellenistic worldview was preserved and absorbed into the Arabic-speaking Muslim world during the Islamic Golden Age. The recovery and assimilation of Greek works and Islamic inquiries into Western Europe from the 10th to 13th century revived the learning of natural philosophy in the West. Traditions of early science were also developed in ancient India and separately in ancient China, the Chinese model having influenced Vietnam, Korea and Japan before Western exploration. Among the Pre-Columbian peoples of Mesoamerica, the Zapotec civilization established their first known traditions of astronomy and mathematics for producing calendars, followed by other civilizations such as the Maya.
Natural philosophy was transformed by the Scientific Revolution that transpired during the 16th and 17th centuries in Europe, as new ideas and discoveries departed from previous Greek conceptions and traditions. The New Science that emerged was more mechanistic in its worldview, more integrated with mathematics, and more reliable and open as its knowledge was based on a newly defined scientific method. More "revolutions" in subsequent centuries soon followed. The chemical revolution of the 18th century, for instance, introduced new quantitative methods and measurements for chemistry. In the 19th century, new perspectives regarding the conservation of energy, age of Earth, and evolution came into focus. And in the 20th century, new discoveries in genetics and physics laid the foundations for new sub disciplines such as molecular biology and particle physics. Moreover, industrial and military concerns as well as the increasing complexity of new research endeavors ushered in the era of "big science," particularly after World War II.

== Approaches to history of science ==

The nature of the history of science - including both the definition of science and whether the English word "science" is a misleading term for pre-modern scholarship as well as non-scholarly knowledge of the natural world - is a topic of ongoing debate and sometimes significant friction between scientists, sociologists and historians. The history of science is often seen as a linear story of progress,
but historians have come to see the story as more complex.
Alfred Edward Taylor has characterised lean periods in the advance of scientific discovery as "periodical bankruptcies of science".
The professionalization of the history of science in the 20th century was accompanied by a prodigious and proliferating specialization, with the field seeming to strive to match the protean diversity of modern science itself. Science is a human activity, and scientific contributions have come from people from a wide range of different backgrounds and cultures. Historians of science increasingly see their field as part of a global history of exchange, conflict and collaboration.
The relationship between science and religion has been variously characterized in terms of "conflict", "harmony", "complexity", and "mutual independence", among others. Events in Europe such as the Galileo affair of the early 17th century led scholars such as John William Draper to postulate (c. 1874) a conflict thesis, suggesting that religion and science have been in conflict methodologically, factually and politically throughout history. The "conflict thesis" has since lost favor among the majority of contemporary scientists and historians of science. However, some contemporary philosophers and scientists, such as Richard Dawkins, still subscribe to this thesis.
Historians have emphasized that trust is necessary for agreement on claims about nature. In this light, the 1660 establishment of the Royal Society and its code of experiment – trustworthy because witnessed by its members – has become an important chapter in the history of science. Many people in modern history (typically women and persons of color) were excluded from elite scientific communities and characterized by the science establishment as inferior. Historians in the 1980s and 1990s described the structural barriers to participation and began to recover the contributions of overlooked individuals. Historians have also investigated the mundane practices of science such as fieldwork and specimen collection, correspondence, drawing, record-keeping, and the use of laboratory and field equipment.

== Prehistory ==

In prehistoric times, knowledge and technique were passed from generation to generation in an oral tradition. For instance, the domestication of maize for agriculture has been dated to about 9,000 years ago in southern Mexico, before the development of writing systems. Similarly, archaeological evidence indicates the development of astronomical knowledge in preliterate societies.
The oral tradition of preliterate societies had several features, the first of which was its fluidity. New information was constantly absorbed and adjusted to new circumstances or community needs. There were no archives or reports. This fluidity was closely related to the practical need to explain and justify a present state of affairs. Another feature was the tendency to describe the universe as just sky and earth, with a potential underworld. They were also prone to identify causes with beginnings, thereby providing a historical origin with an explanation. There was also a reliance on a "medicine man" or "wise woman" for healing, knowledge of divine or demonic causes of diseases, and in more extreme cases, for rituals such as exorcism, divination, songs, and incantations. Finally, there was an inclination to unquestioningly accept explanations that might be deemed implausible in more modern times while at the same time not being aware that such credulous behaviors could have posed problems.
The development of writing enabled humans to store and communicate knowledge across generations with much greater accuracy. Its invention was a prerequisite for the development of philosophy and later science in ancient times. Moreover, the extent to which philosophy and science would flourish in ancient times depended on the efficiency of a writing system (e.g., use of alphabets).

== Ancient Near East and North East Africa ==

The earliest roots of science can be traced to the Ancient Near East and North East Africa c. 3000–1200 BCE – in particular to Ancient Egypt and Mesopotamia.

=== Ancient Egypt ===

Archaeological evidence has suggested that the Ancient Egyptian counting system had origins in Sub-Saharan Africa. Also, fractal geometry designs which are widespread among Sub-Saharan African cultures are also found in Egyptian architecture and cosmological signs.The Ishango bone, according to scholar Alexander Marshack, may have influenced the later development of mathematics in Egypt as, like some entries on the Ishango bone, Egyptian arithmetic also made use of multiplication by 2; this ho


The history of technology is the history of human invention of tools and techniques. Technology includes methods ranging from simple stone tools to the complex genetic engineering and information technology that has emerged since the 1980s. The term technology comes from the Greek words techne, meaning art and craft, and logos, meaning word and speech. It was first used to describe applied arts, but it is now used to describe advancements and changes that affect the environment around us.
New knowledge has enabled people to create new tools. Conversely, many scientific endeavors are made possible by new technologies, such as scientific instruments that allow us to study nature in greater detail than our natural senses can.
Since much of technology is applied science, technical history is connected to the history of science. Since technology uses resources, technical history is tightly connected to economic history. From those resources, technology produces other resources, including technological artifacts used in everyday life. Technological change affects, and is affected by, a society's cultural traditions. It is a force for economic growth and a means of developing and projecting economic, political, and military power and wealth.

== Measuring technological progress ==
Many sociologists and anthropologists have created social theories dealing with social and cultural evolution. Some, such as Lewis H. Morgan, Leslie White, and Gerhard Lenski, have declared technological progress the primary factor driving the development of human civilization. Morgan's concept of three major stages of social evolution (savagery, barbarism, and civilization) can be divided by technological milestones, such as fire. White argued that the measure by which to judge the evolution of culture is energy.
For White, "the primary function of culture" is to "harness and control energy." White differentiates between five stages of human development: In the first, people use the energy of their own muscles. In the second, they use the energy of domesticated animals. In the third, they use plant energy (agricultural revolution). In the fourth, they learn to use the energy of natural resources: coal, oil, gas. In the fifth, they harness nuclear energy. White introduced the formula P = E/T, where P is the development index, E is a measure of energy consumed, and T is a measure of the efficiency of technical factors in using the energy. In his own words, "culture evolves as the amount of energy harnessed per capita per year is increased, or as the efficiency of the instrumental means of putting the energy to work is increased". Nikolai Kardashev extrapolated his theory, creating the Kardashev scale, which categorizes the energy use of advanced civilizations.

Lenski's approach focuses on information. The more information and knowledge (especially the ability to shape the natural environment) a given society has, the more advanced it is. He identifies four stages of human development, based on advances in the history of communication. In the first stage, information is passed by genes. In the second, when humans gain sentience, they can learn and pass information through experience. In the third, the humans start using signs and develop logic. In the fourth, they can create symbols, develop language, and write. Advancements in communications technology translate into advancements in the economic system and political system, distribution of wealth, social inequality, and other spheres of social life. He also differentiates societies based on their level of technology, communication, and economy:
hunter-gatherer,
simple agricultural,
advanced agricultural,
industrial,
special (such as fishing societies).
In economics, productivity is a measure of technological progress. Productivity increases when fewer inputs (classically, labor and capital, though some measures include energy and materials) are used to produce a unit of output. Another indicator of technological progress is the development of new products and services, which is necessary to offset unemployment that would otherwise result from reduced labor inputs. In developed countries, productivity growth has been slowing since the late 1970s; however, it has been higher in some sectors, such as manufacturing. For example, employment in manufacturing in the United States declined from over 30% in the 1940s to just over 10% 70 years later. Similar changes occurred in other developed countries. This stage is referred to as post-industrial.
In the late 1970s sociologists and anthropologists like Alvin Toffler (author of Future Shock), Daniel Bell and John Naisbitt have approached the theories of post-industrial societies, arguing that the current era of industrial society is coming to an end, and services and information are becoming more important than industry and goods. Some extreme visions of post-industrial society, especially in fiction, are strikingly similar to visions of near- and post-singularity societies.

== By period and geography ==
The following is a summary of the history of technology by time period and geography:

=== Prehistory ===

==== Stone Age ====

During most of the Paleolithic – the bulk of the Stone Age – all humans lived with limited tools and few permanent settlements. The first major technologies were tied to survival, hunting, and food preparation. Stone tools and weapons, fire, and clothing were major technological developments during this period.
Human ancestors have been using stone and other tools since long before the emergence of Homo sapiens approximately 300,000 years ago. The earliest direct evidence of tool usage was found in Ethiopia within the Great Rift Valley, dating back to 2.5 million years ago. The earliest methods of stone tool making, known as the Oldowan "industry", date back to at least 2.3 million years ago. This era of stone tool use is called the Paleolithic, or "Old stone age", and spans all of human history up to the development of agriculture approximately 12,000 years ago.
To make a stone tool, a "core" of hard stone with specific flaking properties (such as flint) was struck with a hammerstone. This flaking produced sharp edges which could be used as tools, primarily in the form of choppers or scrapers. These tools greatly aided the early humans in their hunter-gatherer lifestyle to perform a variety of tasks including butchering carcasses (and breaking bones to get at the marrow); chopping wood; cracking open nuts; skinning an animal for its hide, and even forming other tools out of softer materials such as bone and wood.
The earliest stone tools were irrelevant, being little more than a fractured rock. In the Acheulian era, beginning approximately 1.65 million years ago, methods of working these stones into specific shapes, such as hand axes emerged. This early Stone Age is described as the Lower Paleolithic.
The Middle Paleolithic, approximately 300,000 years ago, saw the introduction of the prepared-core technique, in which multiple blades could be rapidly produced from a single core stone. The Upper Paleolithic, beginning approximately 40,000 years ago, saw the introduction of pressure flaking, where a wood, bone, or antler punch could be used to shape a stone very finely.
The end of the last Ice Age, about 10,000 years ago, is taken as the end point of the Upper Paleolithic and the beginning of the Epipaleolithic / Mesolithic. The Mesolithic technology included the use of microliths as composite stone tools, along with wood, bone, and antler tools.
The later Stone Age, during which the rudiments of agricultural technology were developed, is called the Neolithic period. During this period, polished stone tools were made from a variety of hard rocks such as flint, jade, jadeite, and greenstone, largely by working exposures as quarries, but later the valuable rocks were pursued by tunneling underground, the first steps in mining technology. The polished axes were


The history of medicine is both a study of medicine throughout history as well as a multidisciplinary field of study that seeks to explore and understand medical practices, both past and present, throughout human societies.
The history of medicine is the study and documentation of the evolution of medical treatments, practices, and knowledge over time. Medical historians often draw from other humanities fields of study including economics, health sciences, sociology, and politics to better understand the institutions, practices, people, professions, and social systems that have shaped medicine. When a period which predates or lacks written sources regarding medicine, information is instead drawn from archaeological sources. This field tracks the evolution of human societies' approach to health, illness, and injury ranging from prehistory to the modern day, the events that shape these approaches, and their impact on populations.
Early medical traditions include those of Babylon, Egypt, China and India. Invention of the microscope was a consequence of improved understanding, during the Renaissance. Prior to the 19th century, humorism (also known as humoralism) was thought to explain the cause of disease but it was gradually replaced by the germ theory of disease, leading to effective treatments and even cures for many infectious diseases. Military doctors advanced the methods of trauma treatment and surgery. Public health measures were developed especially in the 19th century as the rapid growth of cities required systematic sanitary measures. Advanced research centers opened in the early 20th century, often connected with major hospitals. The mid-20th century was characterized by new biological treatments, such as antibiotics. These advancements, along with developments in chemistry, genetics, and radiography led to modern medicine. Medicine was heavily professionalized in the 20th century, and new careers opened to women as nurses (from the 1870s) and as physicians (especially after 1970).

== Prehistoric medicine ==

Prehistoric medicine is a field of study focused on understanding the use of medicinal plants, healing practices, illnesses, and wellness of humans before written records existed. Although styled prehistoric "medicine", prehistoric healthcare practices were vastly different from what we understand medicine to be in the present era and more accurately refers to studies and exploration of early healing practices.
This period extends across the first use of stone tools by early humans c. 3.3 million years ago to the beginning of writing systems and subsequent recorded history c. 5000 years ago.
As human populations were once scattered across the world, forming isolated communities and cultures that sporadically interacted, a range of archaeological periods have been developed to account for the differing contexts of technology, sociocultural developments, and uptake of writing systems throughout early human societies. Prehistoric medicine is then highly contextual to the location and people in question, creating an ununiform period of study to reflect various degrees of societal development.
Without written records, insights into prehistoric medicine comes indirectly from interpreting evidence left behind by prehistoric humans. One branch of this includes the archaeology of medicine; a discipline that uses a range of archaeological techniques from observing illness in human remains, plant fossils, to excavations to uncover medical practices. There is evidence of healing practices within Neanderthals and other early human species. Prehistoric evidence of human engagement with medicine include the discovery of psychoactive plant sources such as psilocybin mushrooms in c. 6000 BCE Sahara to primitive dental care in c. 11,900 BCE (13,000 BP) Riparo Fredian (present-day Italy) and c. 7000 BCE Mehrgarh (present-day Pakistan).
Anthropology is another academic branch that contributes to understanding prehistoric medicine in uncovering the sociocultural relationships, meaning, and interpretation of prehistoric evidence. The overlap of medicine as both a root to healing the body as well as the spiritual throughout prehistoric periods highlights the multiple purposes that healing practices and plants could potentially have. From proto-religions to developed spiritual systems, relationships of humans and supernatural entities, from Gods to shamans, have played an interwoven part in prehistoric medicine.
A significant example of sophisticated prehistoric self-medication is the case of Ötzi the Iceman (c. 3230 BC). According to archaeologist Patrick Hunt, Ötzi carried a deliberate "prehistoric medical kit" to treat his numerous documented ailments. This kit included Piptoporus betulinus (birch polypore fungus), which Hunt suggests was used as both a vermifuge for intestinal parasites and an antibiotic for his Lyme disease; poppy seeds as an analgesic; sloe berries to treat vertigo and eczema associated with Lyme disease; and sphagnum moss as an antiseptic wound dressing.

== Ancient medicine ==

Ancient history covers time between c. 3000 BCE to c. 500 CE, starting from evidenced development of writing systems to the end of the classical era and beginning of the post-classical period. Sociocultural and technological developments could differ locally from settlement to settlement as well as globally from one society to the next.
Ancient medicine covers a similar period of time and presented a range of similar healing theories from across the world connecting nature, religion, and humans within ideas of circulating fluids and energy. Although prominent scholars and texts detailed well-defined medical insights, their real-world applications were marred by knowledge destruction and loss, poor communication, localized reinterpretations, and subsequent inconsistent applications.

=== Ancient Mesopotamian medicine ===
The Mesopotamian region, covering much of present-day Iraq, Kuwait, Syria, Iran, and Turkey, was dominated by a series of civilisations including Sumer, the earliest known civilisation in the Fertile Crescent region, alongside the Akkadians (including Assyrians and Babylonians). Overlapping ideas of what we now understand as medicine, science, magic, and religion characterised early Mesopotamian healing practices as a hybrid naturalistic and supernatural belief system.
The Sumerians developed one of the earliest known writing systems in the 3rd millennium BCE, and created numerous cuneiform clay tablets regarding their civilisation. These included detailed accounts of drug prescriptions and operations, as well as exorcisms. These were administered and carried out by highly defined professionals including bârû (seers), âs[h]ipu (exorcists), and asû (physician-priests). An example of an early, prescription-like medication appeared in Sumerian during the Third Dynasty of Ur (c. 2112 BCE – c. 2004 BCE).
Following the conquest of the Sumerian civilisation by the Akkadian Empire and the empire's eventual collapse from a number of social and environmental factors, the Babylonian civilisation began to dominate the region. Examples of Babylonian Medicine include the extensive Babylonian medical text, the Diagnostic Handbook, written by the ummânū, or chief scholar, Esagil-kin-apli of Borsippa, in the middle of the 11th century BCE during the reign of the Babylonian king Adad-apla-iddina (1069–1046 BCE).
This medical treatise devoted great attention to the practice of diagnosis, prognosis, physical examination, and remedies. The text contains a list of medical symptoms and often detailed empirical observations along with logical rules used in combining observed symptoms on the body of a patient with their diagnosis and prognosis. Here, clearly developed rationales were developed to understand the causes of disease and injury, supported by theories, agreed upon at the time, of elements we might now understand as natural causes, supernatural magic and r


Philosophy (from Ancient Greek philosophía, lit. 'love of wisdom') is a systematic study of general and fundamental questions concerning topics like existence, knowledge, mind, reason, language, and value. It is a rational and critical inquiry that reflects on its methods and assumptions.
Historically, many of the individual sciences, such as physics and psychology, formed part of philosophy. However, they are considered separate academic disciplines in the modern sense of the term. Influential traditions in the history of philosophy include Western, Arabic–Persian, Indian, and Chinese philosophy. Western philosophy originated in Ancient Greece and covers a wide area of philosophical subfields. A central topic in Arabic–Persian philosophy is the relation between reason and revelation. Indian philosophy combines the spiritual problem of how to reach enlightenment with the exploration of the nature of reality and the ways of arriving at knowledge. Chinese philosophy focuses principally on practical issues about right social conduct, government, and self-cultivation.
Major branches of philosophy are epistemology, ethics, logic, and metaphysics. Epistemology studies what knowledge is and how to acquire it. Ethics investigates moral principles and what constitutes right conduct. Logic is the study of correct reasoning and explores how good arguments can be distinguished from bad ones. Metaphysics examines the most general features of reality, existence, objects, and properties. Other subfields are aesthetics, philosophy of language, philosophy of mind, philosophy of mathematics, philosophy of science, philosophy of religion, philosophy of history, and political philosophy. Within each branch, there are competing schools of philosophy that promote different principles, theories, or methods.
Philosophers use a great variety of methods to arrive at philosophical knowledge. They include conceptual analysis, reliance on common sense and intuitions, use of thought experiments, analysis of ordinary language, description of experience, and critical questioning. Many scientific academic disciplines have associated philosophical subfields, like philosophy of physics and philosophy of biology, examining their fundamental concepts, methods, assumptions and implications. Philosophy is related to and informs many other fields, such as law, business, and journalism, providing an interdisciplinary perspective and addressing their ethical questions.

== Etymology ==
The word philosophy comes from the Ancient Greek term φιλοσοφία (philosophía), meaning 'love of wisdom', from φίλος (phílos, 'loving, friend of') and σοφία (sophía) 'wisdom'. Some sources say that the term was coined by the pre-Socratic philosopher Pythagoras, but this is not certain.
The word entered the English language primarily from Old French and Anglo-Norman starting around 1175 CE. The French philosophie is itself a borrowing from the Latin philosophia. The term philosophy acquired the meanings of "advanced study of the speculative subjects (logic, ethics, physics, and metaphysics)", "deep wisdom consisting of love of truth and virtuous living", "profound learning as transmitted by the ancient writers", and "the study of the fundamental nature of knowledge, reality, and existence, and the basic limits of human understanding".
Before the modern age, the term philosophy was used in a wide sense. It included most forms of rational inquiry, such as the individual sciences, as its subdisciplines. For instance, natural philosophy was a major branch of philosophy. This branch of philosophy encompassed a wide range of fields, including disciplines like physics, chemistry, and biology. An example of this usage is the 1687 book Philosophiæ Naturalis Principia Mathematica by Isaac Newton. This book referred to natural philosophy in its title, but it is today considered a book of physics.
The meaning of philosophy changed toward the end of the modern period when it acquired the more narrow meaning common today. In this new sense, the term is mainly associated with disciplines like metaphysics, epistemology, and ethics. Among other topics, it covers the rational study of reality, knowledge, and values. It is distinguished from other disciplines of rational inquiry such as the empirical sciences and mathematics.

== Conceptions of philosophy ==

=== General conception ===
The practice of philosophy is characterized by several general features: it is a form of rational inquiry, it aims to be systematic, and it tends to critically reflect on its own methods and presuppositions. It requires attentively thinking long and carefully about the provocative, vexing, and enduring problems central to the human condition.
The philosophical pursuit of wisdom involves asking general and fundamental questions. It often does not result in straightforward answers but may help a person to better understand the topic, examine their life, dispel confusion, and overcome prejudices and self-deceptive ideas associated with common sense. For example, Socrates stated that "the unexamined life is not worth living" to highlight the role of philosophical inquiry in understanding one's own existence. And according to Bertrand Russell, "the man who has no tincture of philosophy goes through life imprisoned in the prejudices derived from common sense, from the habitual beliefs of his age or his nation, and from convictions which have grown up in his mind without the cooperation or consent of his deliberate reason."

=== Academic definitions ===

Attempts to provide more precise definitions of philosophy are controversial and are studied in metaphilosophy. Some approaches argue that there is a set of essential features shared by all parts of philosophy. Others see only weaker family resemblances or contend that it is merely an empty blanket term. Precise definitions are often only accepted by theorists belonging to a certain philosophical movement and are revisionistic according to Søren Overgaard et al. in that many presumed parts of philosophy would not deserve the title "philosophy" if they were true.
Some definitions characterize philosophy in relation to its method, like pure reasoning. Others focus on its topic; for example, as the study of the biggest patterns of the world as a whole or as the attempt to answer the big questions. Such an approach is pursued by Immanuel Kant, who holds that the task of philosophy is united by four questions: "What can I know?", "What should I do?", "What may I hope?", and "What is the human being?" Both approaches have the problem that they are usually either too wide, by including non-philosophical disciplines, or too narrow, by excluding some philosophical sub-disciplines.
Many definitions of philosophy emphasize its intimate relation to science. In this sense, philosophy is sometimes understood as a proper science in its own right. According to some naturalistic philosophers, such as W. V. O. Quine, philosophy is an empirical yet abstract science that is concerned with wide-ranging empirical patterns instead of particular observations. Science-based definitions usually face the problem of explaining why philosophy in its long history has not progressed to the same extent or in the same way as the sciences. This problem is avoided by seeing philosophy as an immature or provisional science whose subdisciplines cease to be philosophy once they have fully developed. In this sense, philosophy is sometimes described as "the midwife of the sciences".
Other definitions focus on the contrast between science and philosophy. A common theme among many such conceptions is that philosophy is concerned with meaning, understanding, or the clarification of language. According to one view, philosophy is conceptual analysis, which involves finding the necessary and sufficient conditions for the application of concepts. Another definition characterizes philosophy as thinking about thinking to emphasize its self-critical


Epistemology is the branch of philosophy that examines the nature, origin, and limits of knowledge. Also called the theory of knowledge, it explores different types of knowledge, such as propositional knowledge about facts, practical knowledge in the form of skills, and knowledge by acquaintance as a familiarity through experience. Epistemologists study the concepts of belief, truth, and justification to understand the nature of knowledge. To discover how knowledge arises, they investigate sources of justification, such as perception, introspection, memory, reason, and testimony.
The school of skepticism questions the human ability to attain knowledge, while fallibilism says that knowledge is never certain. Empiricists hold that all knowledge comes from sense experience, whereas rationalists believe that some knowledge does not depend on it. Coherentists argue that a belief is justified if it is consistent with other beliefs. Foundationalists, by contrast, maintain that the justification of basic beliefs does not depend on other beliefs. Internalism and externalism debate whether justification is determined solely by mental states or also by external circumstances.
Separate branches of epistemology focus on knowledge in specific fields, like scientific, mathematical, moral, and religious knowledge. Naturalized epistemology relies on empirical methods and discoveries, whereas formal epistemology uses formal tools from logic. Social epistemology investigates the communal aspect of knowledge, and historical epistemology examines its historical conditions. Epistemology is closely related to psychology, which infers the beliefs people hold from their words and actions, while epistemology studies the norms governing the evaluation of beliefs. It also intersects with fields such as decision theory, education, and anthropology.
Early reflections on the nature, sources, and scope of knowledge are found in ancient Greek, Indian, and Chinese philosophy. The relation between reason and faith was a central topic in the medieval period. The modern era was characterized by the contrasting perspectives of empiricism and rationalism. Epistemologists in the 20th century examined the components, structure, and value of knowledge while integrating insights from the natural sciences and linguistics.

== Definition ==
Epistemology is the philosophical study of knowledge and related concepts, such as justification. Also called theory of knowledge, it examines the nature and types of knowledge. It further investigates the sources of knowledge, like perception, inference, and testimony, to understand how knowledge is created. Another set of questions concerns the extent and limits of knowledge, addressing what people can and cannot know. Central concepts in epistemology include belief, truth, evidence, and reason. As one of the main branches of philosophy, epistemology stands alongside fields like ethics, logic, and metaphysics. The term can also refer to specific positions of philosophers within this branch, as in Plato's epistemology and Immanuel Kant's epistemology.
Epistemology explores how people should acquire beliefs. It determines which beliefs or forms of belief acquisition meet the standards or epistemic goals of knowledge and which ones fail, thereby providing an evaluation of beliefs. The fields of psychology and cognitive sociology are also interested in beliefs and related cognitive processes, but examine them from different perspectives. Unlike epistemology, they study the beliefs people actually have and how people acquire them instead of examining the evaluative norms of these processes. In this regard, epistemology is a normative discipline, whereas psychology and cognitive sociology are descriptive disciplines. Epistemology is relevant to many descriptive and normative disciplines, such as the other branches of philosophy and the sciences, by exploring the principles of how they may arrive at knowledge.
The word epistemology comes from the ancient Greek terms ἐπιστήμη (episteme, meaning knowledge or understanding) and λόγος (logos, meaning study of or reason), literally, the study of knowledge. Despite its ancient roots, the word itself was coined only in the 19th century to designate this field as a distinct branch of philosophy.

== Central concepts ==
Epistemologists examine several foundational concepts to understand their essences and rely on them to formulate theories. Various epistemological disagreements have their roots in disputes about the nature and function of these concepts, like the controversies surrounding the definition of knowledge and the role of justification in it.

=== Knowledge ===

Knowledge is an awareness, familiarity, understanding, or skill. Its various forms all involve a cognitive success through which a person establishes epistemic contact with reality. Epistemologists typically understand knowledge as an aspect of individuals, generally as a cognitive mental state that helps them understand, interpret, and interact with the world. While this core sense is of particular interest to epistemologists, the term also has other meanings. For example, the epistemology of groups examines knowledge as a characteristic of a group of people who share ideas. The term can also refer to information stored in documents and computers.
Knowledge contrasts with ignorance, often simply defined as the absence of knowledge. Knowledge is usually accompanied by ignorance because people rarely have complete knowledge of a field, forcing them to rely on incomplete or uncertain information when making decisions. Even though many forms of ignorance can be mitigated through education and research, certain limits to human understanding result in inevitable ignorance. Some limitations are inherent in the human cognitive faculties themselves, such as the inability to know facts too complex for the human mind to conceive. Others depend on external circumstances when no access to the relevant information exists.
Epistemologists disagree on how much people know, for example, whether fallible beliefs can amount to knowledge or whether absolute certainty is required. The most stringent position is taken by radical skeptics, who argue that there is no knowledge at all.

==== Types ====

Epistemologists distinguish between different types of knowledge. Their primary interest is in knowledge of facts, called propositional knowledge. It is theoretical knowledge that can be expressed in declarative sentences using a that-clause, like "Ravi knows that kangaroos hop". For this reason, it is also called knowledge-that. Epistemologists often understand it as a relation between a knower and a known proposition, in the case above between the person Ravi and the proposition "kangaroos hop". It is use-independent since it is not tied to one specific purpose, unlike practical knowledge. It is a mental representation that embodies concepts and ideas to reflect reality. Because of its theoretical nature, it is typically held that only creatures with highly developed minds, such as humans, possess propositional knowledge.
Propositional knowledge contrasts with non-propositional knowledge in the form of knowledge-how and knowledge by acquaintance. Knowledge-how is a practical ability or skill, like knowing how to read or how to prepare lasagna. It is usually tied to a specific goal and not mastered in the abstract without concrete practice. To know something by acquaintance means to have an immediate familiarity with or awareness of it, usually as a result of direct experiential contact. Examples are "familiarity with the city of Perth", "knowing the taste of tsampa", and "knowing Marta Vieira da Silva personally".

Another influential distinction in epistemology is between a posteriori and a priori knowledge. A posteriori knowledge is knowledge of empirical facts based on sensory experience, like "seeing that the sun is shining" and "smelling that a piece of meat has gon


Ethics is the philosophical study of moral phenomena. Also called moral philosophy, it investigates normative questions about what people ought to do or which behavior is morally right. Its main branches include normative ethics, applied ethics, and metaethics.
Normative ethics aims to find general principles that govern how people should act. Applied ethics examines concrete ethical problems in real-life situations, such as abortion, treatment of animals, and business practices. Metaethics explores the underlying assumptions and concepts of ethics. It asks whether there are objective moral facts, how moral knowledge is possible, and how moral judgments motivate people. Influential normative theories are consequentialism, deontology, and virtue ethics. According to consequentialists, an act is right if it leads to the best consequences. Deontologists focus on acts themselves, saying that they must adhere to duties, like telling the truth and keeping promises. Virtue ethics sees the manifestation of virtues, like courage and compassion, as the fundamental principle of morality.
Ethics is closely connected to value theory, which studies the nature and types of value, like the contrast between intrinsic and instrumental value. Moral psychology is a related empirical field and investigates psychological processes involved in morality, such as reasoning and the formation of character. Descriptive ethics describes the dominant moral codes and beliefs in different societies and considers their historical dimension.
The history of ethics started in the ancient period with the development of ethical principles and theories in ancient Egypt, India, China, and Greece. This period saw the emergence of ethical teachings associated with Hinduism, Buddhism, Confucianism, Daoism, and contributions of philosophers like Socrates and Aristotle. During the medieval period, ethical thought was strongly influenced by religious teachings. In the modern period, this focus shifted to a more secular approach concerned with moral experience, reasons for acting, and the consequences of actions. An influential development in the 20th century was the emergence of metaethics.

== Definition ==

Ethics, also called moral philosophy, is the study of moral phenomena. It is one of the main branches of philosophy and investigates the nature of morality and the principles that govern the moral evaluation of conduct, character traits, and institutions. It examines what obligations people have, what behavior is right and wrong, and how to lead a good life. Some of its key questions are "How should one live?" and "What gives meaning to life?". In contemporary philosophy, ethics is usually divided into normative ethics, applied ethics, and metaethics.
Morality concerns what people ought to do rather than what they actually do, what they want to do, or what social conventions require. As a rational and systematic field of inquiry, ethics studies practical reasons why people should act one way rather than another. Most ethical theories seek universal principles that express a general standpoint of what is objectively right and wrong. In a slightly different sense, the term ethics can also refer to individual ethical theories in the form of a rational system of moral principles, such as Aristotelian ethics, and to a moral code that certain societies, social groups, or professions follow, as in Protestant work ethic and medical ethics.
The English word ethics has its roots in the Ancient Greek word êthos (ἦθος), meaning 'character' and 'personal disposition'. This word gave rise to the Ancient Greek word ēthikós (ἠθικός), which was translated into Latin as ethica and entered the English language in the 15th century through the Old French term éthique. The term morality originates in the Latin word moralis, meaning 'manners' and 'character'. It was introduced into the English language during the Middle English period through the Old French term moralité.
The terms ethics and morality are usually used interchangeably but some philosophers distinguish between the two. According to one view, morality focuses on what moral obligations people have while ethics is broader and includes ideas about what is good and how to lead a meaningful life. Another difference is that codes of conduct in specific areas, such as business and environment, are usually termed ethics rather than morality, as in business ethics and environmental ethics.

== Normative ethics ==

Normative ethics is the philosophical study of ethical conduct and investigates the fundamental principles of morality. It aims to discover and justify general answers to questions like "How should one live?" and "How should people act?", usually in the form of universal or domain-independent principles that determine whether an act is right or wrong. For example, given the particular impression that it is wrong to set a child on fire for fun, normative ethics aims to find more general principles that explain why this is the case, like the principle that one should not cause extreme suffering to the innocent, which may itself be explained in terms of a more general principle. Many theories of normative ethics also aim to guide behavior by helping people make moral decisions.
Theories in normative ethics state how people should act or what kind of behavior is correct. They do not aim to describe how people normally act, what moral beliefs ordinary people have, how these beliefs change over time, or what ethical codes are upheld in certain social groups. These topics belong to descriptive ethics and are studied in fields like anthropology, sociology, and history rather than normative ethics.
Some systems of normative ethics arrive at a single principle covering all possible cases. Others encompass a small set of basic rules that address all or at least the most important moral considerations. One difficulty for systems with several basic principles is that these principles may conflict with each other in some cases and lead to ethical dilemmas.
Distinct theories in normative ethics suggest different principles as the foundation of morality. The three most influential schools of thought are consequentialism, deontology, and virtue ethics. These schools are usually presented as exclusive alternatives, but depending on how they are defined, they can overlap and do not necessarily exclude one another. In some cases, they differ in which acts they see as right or wrong. In other cases, they recommend the same course of action but provide different justifications for why it is right.

=== Consequentialism ===

Consequentialism, also called teleological ethics, says that morality depends on consequences. According to the most common view, an act is right if it brings the best future. This means that there is no alternative course of action that has better consequences. A key aspect of consequentialist theories is that they provide a characterization of what is good and then define what is right in terms of what is good. For example, classical utilitarianism says that pleasure is good and that the action leading to the most overall pleasure is right. Consequentialism has been discussed indirectly since the formulation of classical utilitarianism in the late 18th century. A more explicit analysis of this view happened in the 20th century, when the term was coined by G. E. M. Anscombe.
Consequentialists usually understand the consequences of an action in a very wide sense that includes the totality of its effects. This is based on the idea that actions make a difference in the world by bringing about a causal chain of events that would not have existed otherwise. A core intuition behind consequentialism is that the future should be shaped to achieve the best possible outcome.
The act itself is usually not seen as part of the consequences. This means that if an act has intrinsic value or disvalue, it is not included as a factor. Some consequentialists see


Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the study of deductively valid inferences or logical truths. It examines how conclusions follow from premises based on the structure of arguments alone, independent of their topic and content. Informal logic is associated with informal fallacies, critical thinking, and argumentation theory. Informal logic examines arguments expressed in natural language whereas formal logic uses formal language. When used as a countable noun, the term "a logic" refers to a specific logical formal system that articulates a proof system. Logic plays a central role in many fields, such as philosophy, mathematics, computer science, and linguistics.
Logic studies arguments, which consist of a set of premises that leads to a conclusion. An example is the argument from the premises "it's Sunday" and "if it's Sunday then I don't have to work" leading to the conclusion "I don't have to work." Premises and conclusions express propositions or claims that can be true or false. An important feature of propositions is their internal structure. For example, complex propositions are made up of simpler propositions linked by logical vocabulary like

        ∧

    {\displaystyle \land }

 (and) or

        →

    {\displaystyle \to }

 (if...then). Simple propositions also have parts, like "Sunday" or "work" in the example. The truth of a proposition usually depends on the meanings of all of its parts. However, this is not the case for logically true propositions. They are true only because of their logical structure independent of the specific meanings of the individual parts.
Arguments can be either correct or incorrect. An argument is correct if its premises support its conclusion. Deductive arguments have the strongest form of support: if their premises are true then their conclusion must also be true. This is not the case for ampliative arguments, which arrive at genuinely new information not found in the premises. Many arguments in everyday discourse and the sciences are ampliative arguments. They are divided into inductive and abductive arguments. Inductive arguments are statistical generalizations, such as inferring that all ravens are black based on many individual observations of black ravens. Abductive arguments are inferences to the best explanation, for example, when a doctor concludes that a patient has a certain disease which explains the symptoms they suffer. Arguments that fall short of the standards of correct reasoning often embody fallacies. Systems of logic are theoretical frameworks for assessing the correctness of arguments.
Logic has been studied since antiquity. Early approaches include Aristotelian logic, Stoic logic, Nyaya, and Mohism. Aristotelian logic focuses on reasoning in the form of syllogisms. It was considered the main system of logic in the Western world until it was replaced by modern formal logic, which has its roots in the work of late 19th-century mathematicians such as Gottlob Frege. Today, the most commonly used system is classical logic. It consists of propositional logic and first-order logic. Propositional logic only considers logical relations between full propositions. First-order logic also takes the internal parts of propositions into account, like predicates and quantifiers. Extended logics accept the basic intuitions behind classical logic and apply it to other fields, such as metaphysics, ethics, and epistemology, as frameworks for reasoning about what is possible or necessary, what is or should be, and what is believed or known. Deviant logics, on the other hand, reject certain classical intuitions and provide alternative explanations of the basic laws of logic.

== Definition ==
The word "logic" originates from the Greek word logos, which has a variety of translations, such as reason, discourse, or language. Logic is traditionally defined as the study of the laws of thought or correct reasoning, and is usually understood in terms of inferences or arguments. Reasoning is the activity of drawing inferences. Arguments are the outward expression of inferences. An argument is a set of premises together with a conclusion. Logic is interested in whether arguments are correct, i.e. whether their premises support the conclusion. These general characterizations apply to logic in the widest sense, i.e., to both formal and informal logic since they are both concerned with assessing the correctness of arguments. Formal logic is the traditionally dominant field, and some logicians restrict logic to formal logic.

=== Formal logic ===

Formal logic (also known as symbolic logic) is widely used in mathematical logic. It uses a formal approach to study reasoning: it replaces concrete expressions with abstract symbols to examine the logical form of arguments independent of their concrete content. In this sense, it is topic-neutral since it is only concerned with the abstract structure of arguments and not with their concrete content.
Formal logic is interested in deductively valid arguments, for which the truth of their premises ensures the truth of their conclusion. This means that it is impossible for the premises to be true and the conclusion to be false. For valid arguments, the logical structure that leads from the premises to the conclusion follows a pattern called a rule of inference. For example, modus ponens is a rule of inference according to which all arguments of the form "(1) p, (2) if p then q, (3) therefore q" are valid, independent of what the terms p and q stand for. In this sense, formal logic can be defined as the science of valid inferences. An alternative definition sees logic as the study of logical truths. A proposition is logically true if its truth depends only on the logical vocabulary used in it. This means that it is true in all possible worlds and under all interpretations of its non-logical terms, like the claim "either it is raining, or it is not". These two definitions of formal logic are not identical, but they are closely related. For example, if the inference from p to q is deductively valid then the claim "if p then q" is a logical truth.

Formal logic uses formal languages to express, analyze, and clarify arguments. They normally have a very limited vocabulary and exact syntactic rules. These rules specify how their symbols can be combined to construct sentences, so-called well-formed formulas. This simplicity and exactness of formal logic make it capable of formulating precise rules of inference. They determine whether a given argument is valid. Because of the reliance on formal language, natural language arguments cannot be studied directly. Instead, they need to be translated into formal language before their validity can be assessed.
The term "logic" can also be used in a slightly different sense as a countable noun. In this sense, a logic is a logical formal system. Distinct logics differ from each other concerning the rules of inference they accept as valid and the formal languages used to express them. Starting in the late 19th century, many new formal systems have been proposed. There are disagreements about what makes a formal system a logic. For example, it has been suggested that only logically complete systems, like first-order logic, qualify as logics. For such reasons, some theorists deny that higher-order logics are logics in the strict sense.

=== Informal logic ===

When understood in a wide sense, logic encompasses both formal and informal logic. Informal logic uses non-formal criteria and standards to analyze and assess the correctness of arguments. Its main focus is on everyday discourse. Its development was prompted by difficulties in applying the insights of formal logic to natural language arguments. In this regard, it considers problems that formal logic on its own is unable to address. Both provide criteria for assessing the co


Mathematics is a field of knowledge concerned with abstract concepts such as numbers, geometric shapes, sets, functions, and probabilities. It uses logical reasoning and proof to study and establish their properties, often expressed as theorems, formulas, and equations. Mathematics is used to model and solve problems in science, engineering, technology, economics, and everyday life.
There are many areas of mathematics, including number theory (the study of integers and their properties), algebra (the study of operations and the structures they form), geometry (the study of shapes and spaces that contain them), analysis (the quantitative study of approximation and convergence), and set theory (presently used as a foundation for all mathematics).
Mathematics involves the description and manipulation of abstract objects that are either abstractions from nature or purely abstract entities that are stipulated to have certain properties, called axioms. Mathematics uses pure reason to prove the properties of objects through proofs, which consist of a succession of applications of deductive rules to already established results. These results, called theorems, include previously proved theorems, axioms, and—in case of abstraction from nature—some basic properties that are considered true starting points of the theory under consideration.
Mathematics is essential in the natural sciences, engineering, medicine, finance, computer science, and the social sciences. Although mathematics is widely used to model empirical phenomena, its results are established by deductive proof rather than by experiment. The relationship between mathematical truth, logic, and reality is  a subject of philosophical debate. Some areas of mathematics, such as game theory, are developed in close correlation with their applications and are often grouped under applied mathematics. Other areas are developed independently from any application but often find practical applications later.
Mathematical written records first appeared in Ancient Egypt and Mesopotamia, but the concept of proof and its associated mathematical rigor began in Ancient Greek mathematics, exemplified in Euclid's Elements. Mathematics was primarily divided into geometry and arithmetic until the 16th and 17th centuries, when algebra and infinitesimal calculus evolved into new fields. Since then, the interaction between mathematical innovations and scientific discoveries has led to a correlated increase in the development of both. At the end of the 19th century, the foundational crisis of mathematics led to the systematic use of the axiomatic method, which heralded a dramatic increase in the number of mathematical areas and their fields of application. The contemporary Mathematics Subject Classification lists more than sixty first-level areas of mathematics.

== Areas of mathematics ==

Before the Renaissance, mathematics was divided into two main areas: arithmetic, regarding the study and manipulation of numbers, and geometry, regarding the study of shapes. Some types of pseudoscience, such as numerology and astrology, were not then clearly distinguished from mathematics.
Beginning with the Renaissance, two more areas became predominant. New mathematical notation led to modern algebra which, roughly speaking, begins with the study and manipulation of algebraic expressions. Calculus, consisting of the two subfields differential calculus and integral calculus, originated with geometry but evolved into the study of continuous functions, which model the typically nonlinear relationships between varying quantities, as represented by variables. This division into four main areas—arithmetic, geometry, algebra, and calculus—endured until the end of the 19th century. Other areas that were previously studied by mathematicians, such as celestial mechanics and solid mechanics, are now considered as belonging to physics. The subject of combinatorics has been studied for much of recorded history, yet did not become a separate branch of mathematics until the 17th century.
At the end of the 19th century, the foundational crisis in mathematics and the systematic use of the axiomatic method led to an explosion of new areas of mathematics. The 2020 Mathematics Subject Classification contains no less than sixty-three first-level areas. Some of these areas correspond to the older division, as is true regarding number theory (the modern name for higher arithmetic) and geometry. Several other first-level areas have "geometry" in their names or are otherwise commonly considered part of geometry. Algebra and calculus do not appear as first-level areas but are split into several first-level areas. Other first-level areas emerged during the 20th century or had not previously been considered as mathematics, such as mathematical logic and foundations.

=== Number theory ===

Number theory evolved from the manipulation of numbers, that is, natural numbers

        (

          N

        )
        ,

    {\displaystyle (\mathbb {N} ),}

 and later expanded to integers

        (

          Z

        )

    {\displaystyle (\mathbb {Z} )}

 and rational numbers

        (

          Q

        )
        .

    {\displaystyle (\mathbb {Q} ).}

 Number theory was once called arithmetic, but nowadays this term is mostly used for numerical calculations. The study of numbers arguably dates back to ancient Babylon and probably China, but developed into a distinct discipline in Ancient Greece. Two prominent early number theorists were Euclid and Diophantus of Alexandria. The modern study of number theory in its abstract form is largely attributed to Pierre de Fermat and Leonhard Euler. The field came to full fruition with the contributions of Adrien-Marie Legendre and Carl Friedrich Gauss.
Many easily stated number problems have solutions that require sophisticated methods, often from across mathematics. A prominent example is Fermat's Last Theorem. This conjecture was stated in 1637 by Pierre de Fermat, but it was proved only in 1994 by Andrew Wiles, who used tools including scheme theory from algebraic geometry, category theory, and homological algebra. Another example is Goldbach's conjecture, which asserts that every even integer greater than 2 is the sum of two prime numbers. Stated in 1742 by Christian Goldbach, it remains unproven despite considerable effort.
Number theory includes several subareas, including analytic number theory, algebraic number theory, geometry of numbers (method oriented), Diophantine analysis, and transcendence theory (problem oriented).

=== Geometry ===

Geometry is one of the oldest branches of mathematics. It started with empirical recipes concerning shapes, such as lines, angles and circles, which were developed mainly for the needs of surveying and architecture, but has since blossomed out into many other subfields.
A fundamental innovation was the ancient Greeks' introduction of the concept of proofs, which require that every assertion must be proved. For example, it is not sufficient to verify by measurement that, say, two lengths are equal; their equality must be proven via reasoning from previously accepted results (theorems) and a few basic statements. The basic statements are not subject to proof because they are self-evident (postulates), or are part of the definition of the subject of study (axioms). This principle, foundational for all mathematics, was first elaborated for geometry, and was systematized by Euclid around 300 BC in his book Elements.
The resulting Euclidean geometry is the study of shapes and their arrangements constructed from lines, planes and circles in the Euclidean plane (plane geometry) and the three-dimensional Euclidean space.
Euclidean geometry was developed without change of methods or scope until the 17th century, when René Descartes introduced what is


Physics is the scientific study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. It is one of the most fundamental scientific disciplines. A scientist who specializes in the field of physics is called a physicist.
Physics is one of the oldest academic disciplines. Over much of the past two millennia, physics, chemistry, biology, and certain branches of mathematics were part of natural philosophy, but during the Scientific Revolution in the 17th century, these natural sciences branched into separate research endeavors. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in these and other academic disciplines, such as mathematics and philosophy.
Advances in physics often enable new technologies. For example, advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led directly to the development of technologies that have transformed modern society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus.

== History ==

The word physics comes from the Latin physica ('study of nature'), which itself is a borrowing of the Greek φυσική (phusikḗ 'natural science'), a term derived from φύσις (phúsis 'origin, nature, property').

=== Ancient astronomy ===

Astronomy is one of the oldest natural sciences. Early civilizations dating before 3000 BCE, such as the Sumerians, ancient Egyptians, and the Indus Valley Civilization, had a predictive knowledge and a basic awareness of the motions of the Sun, Moon, and stars. The stars and planets, believed to represent gods, were often worshipped. While the explanations for the observed positions of the stars were often unscientific and lacking in evidence, these early observations laid the foundation for later astronomy, as the stars were found to traverse great circles across the sky, which could not explain the positions of the planets.
According to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descended from late Babylonian astronomy. Egyptian astronomers left monuments showing knowledge of the constellations and the motions of the celestial bodies, while Greek poet Homer wrote of various celestial objects in his Iliad and Odyssey; later Greek astronomers provided names, which are still used today, for most constellations visible from the Northern Hemisphere.

=== Natural philosophy ===

Natural philosophy has its origins in Greece during the Archaic period (650 BCE – 480 BCE), when pre-Socratic philosophers like Thales rejected non-naturalistic explanations for natural phenomena and proclaimed that every event had a natural cause. They proposed ideas verified by reason and observation, and many of their hypotheses proved successful in experiment; for example, atomism was found to be correct approximately 2000 years after it was proposed by Leucippus and his pupil Democritus.

=== Aristotle and Hellenistic physics ===

During the classical period in Greece (6th, 5th and 4th centuries BCE) and in Hellenistic times, natural philosophy developed along many lines of inquiry. Aristotle (Greek: Ἀριστοτέλης, Aristotélēs) (384–322 BCE), a student of Plato,
wrote on many subjects, including a substantial treatise on "Physics" – in the 4th century BC. Aristotelian physics was influential for about two millennia. His approach mixed some limited observation with logical deductive arguments, but did not rely on experimental verification of deduced statements. Aristotle's foundational work in Physics, though very imperfect, formed a framework against which later thinkers further developed the field. His approach is entirely superseded today.
He explained ideas such as motion (and gravity) with the theory of four elements.
Aristotle believed that each of the four classical elements (air, fire, water, earth) had its own natural place. Because of their differing densities, each element will revert to its own specific place in the atmosphere. So, because of their weights, fire would be at the top, air underneath fire, then water, then lastly earth. He also stated that when a small amount of one element enters the natural place of another, the less abundant element will automatically go towards its own natural place. For example, if there is a fire on the ground, the flames go up into the air in an attempt to go back into its natural place where it belongs. His laws of motion included: that heavier objects will fall faster, the speed being proportional to the weight and the speed of the object that is falling depends inversely on the density object it is falling through (e.g. density of air). He also stated that, when it comes to violent motion (motion of an object when a force is applied to it by a second object), the speed that object moves will only be as fast or strong as the measure of force applied to it. The problem of motion and its causes was studied carefully, leading to the philosophical notion of a "prime mover" as the ultimate source of all motion in the world (Book 8 of his treatise Physics).

=== Medieval European and Islamic ===

The Western Roman Empire fell to invaders and internal decay in the fifth century, resulting in a decline in intellectual pursuits in western Europe. By contrast, the Eastern Roman Empire (usually known as the Byzantine Empire) resisted the attacks from invaders and continued to advance various fields of learning, including physics. In the sixth century, John Philoponus challenged the dominant Aristotelian approach to science although much of his work was focused on Christian theology.
In the sixth century, Isidore of Miletus created an important compilation of Archimedes' works that are copied in the Archimedes Palimpsest.
Islamic scholarship inherited Aristotelian physics from the Greeks and during the Islamic Golden Age developed it further.
The most notable innovations under Islamic scholarship were in the field of optics and vision, which came from the works of many scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna. In his Book of Optics (also known as Kitāb al-Manāẓir) Ibn al-Haytham presented the idea of light rays as an alternative to the ancient Greek idea about visual rays. Like Ptolemy, Ibn al-Haytham applied controlled experiments, verifying the laws of refraction and reflection with the new concept of light rays, but still lacking the concept of image formation.

=== Scientific Revolution ===

Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover what are now considered to be the laws of physics.
Major developments in this period include the replacement of the geocentric model of the Solar System with the heliocentric Copernican model, the laws governing the motion of planetary bodies (determined by Johannes Kepler between 1609 and 1619), Galileo's pioneering work on telescopes and observational astronomy in the 16th and 17th centuries, and Isaac Newton's discovery and unification of the laws of motion and universal gravitation (that would come to bear his name). Newton, and separately Gottfried Wilhelm Leibniz, developed calculus, the mathematical study of continuous change, and Newton applied it to solve physical problems.

=== 19th century ===

The discovery of laws in thermodynamics, chemistry, and electromagnetics resulted from research efforts during the Industrial Revolution as energy needs increased. By the end of the 19th century, theories of thermodynamics, mechanics, and electromagnetics matched a


Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies matter: composition, structure, properties, behavior and the changes they undergo during reactions with other substances. Chemistry also addresses the nature of chemical bonds in chemical compounds.
In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant growth (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the properties of the soil on the Moon (cosmochemistry), how medications work (pharmacology), and how to collect DNA evidence at a crime scene (forensics).
Chemistry has existed under various names since ancient times. It has evolved, and now chemistry encompasses various areas of specialisation, or subdisciplines, that continue to increase in number and interrelate to create further interdisciplinary fields of study. The applications of various fields of chemistry are used frequently for economic purposes in the chemical industry.

== Etymology ==

The word chemistry comes from a modification during the Renaissance of the word alchemy, which referred to an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism, and medicine. Alchemy is often associated with the quest to turn lead or other base metals into gold, though alchemists were also interested in many of the questions of modern chemistry.
The modern word alchemy in turn is derived from the Arabic word al-kīmīā (الكیمیاء). This may have Egyptian origins since al-kīmīā is derived from the Ancient Greek χημία, which is in turn derived from the word Kemet, which is the ancient name of Egypt in the Egyptian language. Alternately, al-kīmīā may derive from χημεία 'cast together'.

== Modern principles ==

The current model of atomic structure is the quantum mechanical model. Traditional chemistry starts with the study of elementary particles, atoms, molecules, substances, metals, crystals and other aggregates of matter. Matter can be studied in solid, liquid, gas and plasma states, in isolation or in combination. The interactions, reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory.
The chemistry laboratory stereotypically uses various forms of laboratory glassware. However glassware is not central to chemistry, and a great deal of experimental (as well as applied/industrial) chemistry is done without it.

A chemical reaction is a transformation of some substances into one or more different substances. The basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation, which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal. (When the number of atoms on either side is unequal, the transformation is referred to as a nuclear reaction or radioactive decay.) The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.
Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure, phase, as well as their chemical compositions. They can be analyzed using the tools of chemical analysis, e.g. spectroscopy and chromatography. Scientists engaged in chemical research are known as chemists. Most chemists specialize in one or more sub-disciplines. Several concepts are essential for the study of chemistry; some of them are:

=== Matter ===

In chemistry, matter is defined as anything that has rest mass and volume (it takes up space) and is made up of particles. The particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon. Matter can be a pure chemical substance or a mixture of substances.

==== Atom ====

The atom is the basic unit of chemistry. It consists of a dense core called the atomic nucleus surrounded by a space occupied by an electron cloud. The nucleus is made up of positively charged protons and uncharged neutrons (together called nucleons), while the electron cloud consists of negatively charged electrons which orbit the nucleus. In a neutral atom, the negatively charged electrons balance out the positive charge of the protons. The nucleus is dense; the mass of a nucleon is approximately 1,836 times that of an electron, yet the radius of an atom is about 10,000 times that of its nucleus.
The atom is also the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s), coordination number, and preferred types of bonds to form (e.g., metallic, ionic, covalent).

==== Element ====

A chemical element is a pure substance which is composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z. The mass number is the sum of the number of protons and neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same atomic number, they may not necessarily have the same mass number; atoms of an element which have different mass numbers are known as isotopes. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, but atoms of carbon may have mass numbers of 12 or 13.
The standard presentation of the chemical elements is in the periodic table, which orders elements by atomic number. The periodic table is arranged in groups, or columns, and periods, or rows. The periodic table is useful in identifying periodic trends.

==== Compound ====

A compound is a pure chemical substance composed of more than one element. The properties of a compound bear little similarity to those of its elements. The standard nomenclature of compounds is set by the International Union of Pure and Applied Chemistry (IUPAC). Organic compounds are named according to the organic nomenclature system. The names for inorganic compounds are created according to the inorganic nomenclature system. When a compound has more than one component, then they are divided into two classes, the electropositive and the electronegative components. In addition the Chemical Abstracts Service (CAS) has devised a method to index chemical substances. In this scheme each chemical substance is identifiable by a number known as its CAS registry number.

==== Molecule ====

A molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances (see below). Molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs.
Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires


Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, origin, evolution, and distribution of life. Central to biology are five fundamental themes: the cell as the basic unit of life, genes and heredity as the basis of inheritance, evolution as the driver of biological diversity, energy transformation for sustaining life processes, and homeostasis, the maintenance of internal stability.
Biology examines life across multiple levels of organization, from molecules and cells to organisms, population, and ecosystems. Subdisciplines include molecular biology, physiology, ecology, evolutionary biology, developmental biology, and systematics, among others. Each of these fields applies a range of methods to investigate biological phenomena, including observation, experimentation, and mathematical modeling. Modern biology is grounded in the theory of evolution by natural selection, first articulated by Charles Darwin, and in the molecular understanding of genes encoded in DNA. The discovery of the structure of DNA and advances in molecular genetics have transformed many areas of biology, leading to applications in medicine, agriculture, biotechnology, and environmental science.
Biologists classify organisms—from single-celled archaea and bacteria to multicellular plants, fungi, and animals—based on shared characteristics and evolutionary relationships, using taxonomic and phylogenetics.

== Etymology ==
From Greek βίος (bíos) 'life', (from Proto-Indo-European root *gwei-, to live) and λογία (logia) 'study of'. The compound appears in the title of Volume 3 of Michael Christoph Hanow's Philosophiae naturalis sive physicae dogmaticae: Geologia, biologia, phytologia generalis et dendrologia, published in 1766. The term biology in its modern sense appears to have been introduced independently by Thomas Beddoes (in 1799), Karl Friedrich Burdach (in 1800), Gottfried Reinhold Treviranus (Biologie oder Philosophie der lebenden Natur, 1802) and Jean-Baptiste Lamarck (Hydrogéologie, 1802).

== History ==

The earliest of roots of science, which included medicine, can be traced to ancient Egypt and Mesopotamia in around 3000 to 1200 BCE. Their contributions shaped ancient Greek natural philosophy. Ancient Greek philosophers such as Aristotle (384–322 BCE) contributed extensively to the development of biological knowledge. He explored biological causation and the diversity of life. His successor, Theophrastus, began the scientific study of plants. Scholars of the medieval Islamic world who wrote on biology included al-Jahiz (781–869), Al-Dīnawarī (828–896), who wrote on botany.
Biology began to develop quickly with Anton van Leeuwenhoek's dramatic improvement of the microscope. It was then that scholars discovered spermatozoa, bacteria, infusoria and the diversity of microscopic life. Investigations by Jan Swammerdam led to new interest in entomology and helped to develop techniques of microscopic dissection and staining. Advances in microscopy had a profound impact on biological thinking. In the early 19th century, biologists pointed to the central importance of the cell. In 1838, Schleiden and Schwann began promoting the now universal ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of life, although they opposed the idea that (3) all cells come from the division of other cells, continuing to support spontaneous generation. However, Robert Remak and Rudolf Virchow were able to reify the third tenet, and by the 1860s most biologists accepted all three tenets which consolidated into cell theory.
Meanwhile, taxonomy and classification became the focus of natural historians. Carl Linnaeus published a basic taxonomy for the natural world in 1735, and in the 1750s introduced scientific names for all his species. Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—even suggesting the possibility of common descent.

Serious evolutionary thinking originated with the works of Jean-Baptiste Lamarck, who presented a coherent theory of evolution. The British naturalist Charles Darwin, combining the biogeographical approach of Humboldt, the uniformitarian geology of Lyell, Malthus's writings on population growth, and his own morphological expertise and extensive natural observations, forged a more successful evolutionary theory based on natural selection; similar reasoning and evidence led Alfred Russel Wallace to independently reach the same conclusions.
The basis for modern genetics began with the work of Gregor Mendel in 1865. This outlined the principles of biological inheritance. However, the significance of his work was not realized until the early 20th century when evolution became a unified theory as the modern synthesis reconciled Darwinian evolution with classical genetics. In the 1940s and early 1950s, a series of experiments by Alfred Hershey and Martha Chase pointed to DNA as the component of chromosomes that held the trait-carrying units that had become known as genes. A focus on new kinds of model organisms such as viruses and bacteria, along with the discovery of the double-helical structure of DNA by James Watson and Francis Crick in 1953, marked the transition to the era of molecular genetics. From the 1950s onwards, biology has been vastly extended in the molecular domain. The genetic code was cracked by Har Gobind Khorana, Robert W. Holley and Marshall Warren Nirenberg after DNA was understood to contain codons. The Human Genome Project was launched in 1990 to map the human genome.

== Fields ==

=== Biochemistry ===
Biochemistry is the study of chemical processes within and relating to living organisms.

=== Molecular biology ===
Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells. It is centered largely on the study of nucleic acids (such as DNA and RNA) and proteins. It examines the structure, function, and interactions of these macromolecules as they orchestrate processes such as replication, transcription, translation, protein synthesis, and complex biomolecular interactions.
In 1953, the Miller–Urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early Earth, thus suggesting that complex organic molecules could have arisen spontaneously in early Earth in the process of abiogenesis.

=== Cell biology ===

Cell biology is the branch of biology that studies the structure, function, and behaviour of cells.
Bioenergetics is a field in biochemistry and cell biology that concerns energy flow through living systems. This is an active area of biological research that includes the study of the transformation of energy in living organisms and the study of thousands of different cellular processes such as cellular respiration and other metabolic and enzymatic processes that enable the use of energy.

=== Genetics ===

Genetics is the scientific study of inheritance. Classical genetics, specifically, is the study of how genes and traits are passed on from parents to offspring; its principles are called Mendelian inheritance. A Punnett square can be used to predict the results of a test cross. The chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by Thomas Morgans's experiments with fruit flies, which established the sex linkage between eye color and sex in these insects.

=== Evolutionary developmental biology ===

Evolutionary developmental biology compares the developmental processes of different organisms to infer how developmental processes evolved. The field grew from 19th-century beginnings, where embryology faced a mystery: zoologists did not know how embryonic development was controlled


Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is the branch of astronomy that studies the universe as a whole.
Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptians, Babylonians, Greeks, Indians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars.
Astronomy is one of the few sciences in which amateurs play an active role. This is especially true for the discovery and observation of transient events. Amateur astronomers have helped with many important discoveries, such as finding new comets.

== Etymology ==
Astronomy (from the Greek ἀστρονομία from ἄστρον astron, "star" and -νομία -nomia from νόμος nomos, "law" or "rule") means study of celestial objects. Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. The two fields share a common origin but became distinct, astronomy being supported by physics while astrology is not.

=== Use of terms "astronomy" and "astrophysics" ===
"Astronomy" and "astrophysics" are broadly synonymous in modern usage. In dictionary definitions, "astronomy" is "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties", while "astrophysics" is the branch of astronomy dealing with "the behavior, physical properties, and dynamic processes of celestial objects and phenomena". Sometimes, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" means the qualitative study of the subject, whereas "astrophysics" is the physics-oriented version of the subject. Some fields, such as astrometry, are in this sense purely astronomy rather than also astrophysics. Research departments may use "astronomy" and "astrophysics" according to whether the department is historically affiliated with a physics department, and many professional astronomers have physics rather than astronomy degrees. Thus, in modern use, the two terms are often used interchangeably.

== History ==

=== Pre-historic ===

The initial development of astronomy was driven by practical needs like agricultural calendars. Before recorded history archeological sites such as Stonehenge provide evidence of ancient interest in astronomical observations.
Evidence also comes from artefacts such as the Nebra sky disc inlaid with symbols interpreted as a sun, moon, and stars including a cluster of seven stars. Megalithic structures located in Nabta Playa, Upper Egypt featured astronomical calendar arrangements in alignment with the heliacal rising of Sirius and supported calibration the yearly calendar for the annual Nile flood.

=== Classical ===

Civilizations such as Egypt, Mesopotamia, Greece, India, China independently but with cross-cultural influences created astronomical observatories and developed ideas on the nature of the Universe, along with calendars and astronomical instruments. A key early development was the beginning of mathematical and scientific astronomy among the Babylonians, laying the foundations for astronomical traditions in other civilizations. The Babylonians discovered that lunar eclipses recurred in the saros cycle of 223 synodic months.
Following the Babylonians, significant advances were made in ancient Greece and the Hellenistic world. Greek astronomy sought a rational, physical explanation for celestial phenomena.  In the 4th century BC, Heracleides Ponticus was the first to proposed that the Earth rotates on its own axis. In the 3rd century BC, Aristarchus of Samos estimated the size and distance of the Moon and Sun, and he proposed a model of the Solar System where the Earth and planets rotated around the Sun, now called the heliocentric model. In the 2nd century BC, Hipparchus calculated the size and distance of the Moon and invented the earliest known astronomical devices such as the astrolabe. He also observed the small drift in the positions of the equinoxes and solstices with respect to the fixed stars that we now know is caused by precession. Hipparchus also created a catalog of 1020 stars, and most of the constellations of the northern hemisphere derive from Greek astronomy. The Antikythera mechanism (c. 150–80 BC) was an early analog computer designed to calculate the location of the Sun, Moon, and planets for a given date. Technological artifacts of similar complexity did not reappear until the 14th century, when mechanical astronomical clocks appeared in Europe.

=== Post-classical ===
After the classical Greek era, astronomy was dominated by the geocentric model of the Universe, or the Ptolemaic system, named after Claudius Ptolemy. His 13-volume astronomy work, named the Almagest in its Arabic translation, became the primary reference for over a thousand years.  In this system, the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. While the system would eventually be discredited, it gave the most accurate predictions for the positions of astronomical bodies available at that time.
With the arrival of Hellenistic astronomy in India through trade and cultural contacts, Indian astronomy entered a new phase during the early centuries CE.  Earlier indigenous traditions, such as those recorded in the Vedāṅga Jyotiṣa, provided calendrical foundations, while Greek astronomical models were later integrated by scholars including Āryabhaṭa, Varāhamihira, and Brahmagupta. Āryabhaṭa notably improved methods for calculating planetary motions and eclipses. In the later medieval period, the Kerala school contributed to astronomy through refined observational practices and more accurate planetary and eclipse calculations.

Astronomy flourished in the medieval Islamic world. Astronomical observatories were established there by the early 9th century. In 964, the Andromeda Galaxy, the largest galaxy in the Local Group, was described by the Persian Muslim astronomer Abd al-Rahman al-Sufi in his Book of Fixed Stars. The SN 1006 supernova, the brightest apparent magnitude stellar event in the last 1000 years, was observed by the Egyptian Arabic astronomer Ali ibn Ridwan and Chinese astronomers in 1006. Iranian scholar Al-Biruni observed that, contrary to Ptolemy, the Sun's apogee (highest point in the heavens) was mobile, not fixed. Arabic astronomers introduced many Arabic names now used for individual stars.
The ruins at Great Zimbabwe and Timbuktu may have housed astronomical observatories. In Post-classical West Africa, astronomers studied the movement of stars and relation to seasons, crafting charts of the heavens and diagrams of orbits of the other planets based on complex mathematical calculations. Songhai historian Mahmud Kati documented a meteor shower in 1583.
In medieval Europe, Richard of Wallingford (1292–1336) invented the first astronomical clock, the Rectangulus which allowed for the measurement of angles between planets and other astronomical bodies, as well as an equatorium called the Albion which could be used for astronomical calculations such as lunar, solar and planetary longitudes. Nicole Oresme (1320–1382) discussed evidence for the rotation of the Earth. Jean Buridan (1300–1361) developed the theory of impetus, descri