metaphysics

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Metaphysics is the branch of
philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. Some ...
that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of
consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scient ...
and the relationship between
mind The mind is the set of faculties responsible for all mental Phenomenon, phenomena. Often the term is also identified with the phenomena themselves. These faculties include thought, imagination, memory, Will (philosophy), will, and Sensation (psy ...
and
matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic partic ...
, between
substance Substance may refer to: * Matter, anything that has mass and takes up space Chemistry * Chemical substance, a material with a definite chemical composition * Drug substance ** Substance abuse, drug-related healthcare and social policy diagnosis o ...
and attribute, and between potentiality and actuality. The word "metaphysics" comes from two Greek words that, together, literally mean "after or behind or among he study ofthe natural". It has been suggested that the term might have been coined by a first century CE editor who assembled various small selections of
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical Greece, Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatet ...
's works into the treatise we now know by the name ''Metaphysics'' (μετὰ τὰ φυσικά, ''meta ta physika'', 'after the ''Physics'' ', another of Aristotle's works). Metaphysics studies questions related to what it is for something to exist and what types of existence there are. Metaphysics seeks to answer, in an abstract and fully general manner, the questions of: * What * What it is Topics of metaphysical investigation include existence, objects and their properties,
space Space is the boundless Three-dimensional space, three-dimensional extent in which Physical body, objects and events have relative position (geometry), position and direction (geometry), direction. In classical physics, physical space is often ...
and
time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...
, cause and effect, and possibility. Metaphysics is considered one of the four main branches of philosophy, along with
epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Epis ...
,
logic Logic is the study of correct reasoning. It includes both Mathematical logic, formal and informal logic. Formal logic is the science of Validity (logic), deductively valid inferences or of logical truths. It is a formal science investigating h ...
, and
ethics Ethics or moral philosophy is a branch of philosophy that "involves systematizing, defending, and recommending concepts of morality, right and wrong action (philosophy), behavior".''Internet Encyclopedia of Philosophy'' The field of ethics, alo ...
.

# Etymology

The word "metaphysics" derives from the Greek words μετά ('' metá'', "after") and φυσικά (''physiká'', "physics"). It was first used as the title for several of
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical Greece, Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatet ...
's works, because they were usually anthologized after the works on
physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Physical science is that depar ...
in complete editions. The prefix ''meta-'' ("after") indicates that these works come "after" the chapters on physics. However, Aristotle himself did not call the subject of these books metaphysics: he referred to it as "first philosophy" ( el, πρώτη φιλοσοφία; la, philosophia prima). The editor of Aristotle's works, Andronicus of Rhodes, is thought to have placed the books on first philosophy right after another work, ''Physics'', and called them (''tà metà tà physikà biblía'') or "the books hat comeafter the ooks onphysics". However, once the name was given, the commentators sought to find other reasons for its appropriateness. For instance,
Thomas Aquinas Thomas Aquinas, Dominican Order, OP (; it, Tommaso d'Aquino, lit=Thomas of Aquino, Italy, Aquino; 1225 – 7 March 1274) was an Italian Dominican Order, Dominican friar and Catholic priest, priest who was an influential List of Catholic philo ...
understood it to refer to the chronological or pedagogical order among our philosophical studies, so that the "metaphysical sciences" would mean "those that we study after having mastered the sciences that deal with the physical world". The term was misread by other medieval commentators, who thought it meant "the science of what is beyond the physical". Following this tradition, the prefix ''meta-'' has more recently been prefixed to the names of sciences to designate higher sciences dealing with ulterior and more fundamental problems: hence metamathematics, metaphysiology, etc. A person who creates or develops metaphysical theories is called a ''metaphysician''. Common parlance also uses the word ''metaphysics'' for a different referent from that of those already mentioned, namely for beliefs in arbitrary non-physical or magical entities. For example, "metaphysical healing" to refer to healing by means of remedies that are magical rather than scientific. This usage stemmed from the various historical schools of speculative metaphysics which operated by postulating all manner of physical, mental and spiritual entities as bases for particular metaphysical systems. Metaphysics as a subject does not preclude beliefs in such magical entities but neither does it promote them. Rather, it is the subject which provides the vocabulary and logic with which such beliefs might be analyzed and studied, for example to search for inconsistencies both within themselves and with other accepted systems such as
science Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earli ...
.

# Epistemological foundation

Metaphysical study is conducted using deduction from that which is known '' a priori''. Like foundational mathematics (which is sometimes considered a special case of metaphysics applied to the existence of number), it tries to give a coherent account of the structure of the world, capable of explaining our everyday and scientific perception of the world, and being free from contradictions. In mathematics, there are many different ways to define numbers; similarly, in metaphysics, there are many different ways to define objects, properties, concepts, and other entities that are claimed to make up the world. While metaphysics may, as a special case, study the entities postulated by fundamental science such as atoms and superstrings, its core topic is the set of categories such as object, property and causality which those scientific theories assume. For example: claiming that "electrons have charge" is espousing a scientific theory; while exploring what it means for electrons to be (or at least, to be perceived as) "objects", charge to be a "property", and for both to exist in a topological entity called "space," is the task of metaphysics. There are two broad stances about what is "the world" studied by metaphysics. According to metaphysical realism, the objects studied by metaphysics exist independently of any observer so that the subject is the most fundamental of all sciences. Metaphysical anti-realism, on the other hand, assumes that the objects studied by metaphysics exist inside the mind of an observer, so the subject becomes a form of introspection and conceptual analysis. This position is of more recent origin. Some philosophers, notably Kant, discuss both of these "worlds" and what can be inferred about each one. Some, such as the logical positivists, and many scientists, reject the metaphysical realism as meaningless and unverifiable. Others reply that this criticism also applies to any type of knowledge, including hard science, which claims to describe anything other than the contents of human perception, and thus that the world of perception ''is'' the objective world in some sense. Metaphysics itself usually assumes that some stance has been taken on these questions and that it may proceed independently of the choice—the question of which stance to take belongs instead to another branch of philosophy,
epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Epis ...
.

# Central questions

## Ontology (being)

''Ontology'' is the branch of
philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. Some ...
that studies concepts such as existence,
being In metaphysics, ontology is the philosophy, philosophical study of being, as well as related concepts such as existence, Becoming (philosophy), becoming, and reality. Ontology addresses questions like how entities are grouped into Category ...
, becoming, and reality. It includes the questions of how entities are grouped into basic categories and which of these entities exist on the most fundamental level. Ontology is sometimes referred to as the ''science of being''. It has been characterized as ''general metaphysics'' in contrast to ''special metaphysics'', which is concerned with more particular aspects of being. Ontologists often try to determine what the ''categories'' or ''highest kinds'' are and how they form a ''system of categories'' that provides an encompassing classification of all entities. Commonly proposed categories include substances, properties, relations, states of affairs and events. These categories are characterized by fundamental ontological concepts, like ''particularity'' and ''universality'', ''abstractness'' and ''concreteness'' or ''possibility'' and ''necessity''. Of special interest is the concept of ''ontological dependence'', which determines whether the entities of a category exist on the ''most fundamental level''. Disagreements within ontology are often about whether entities belonging to a certain category exist and, if so, how they are related to other entities.

## Identity and change

Identity is a fundamental metaphysical concern. Metaphysicians investigating identity are tasked with the question of what, exactly, it means for something to be identical to itself, or – more controversially – to something else. Issues of identity arise in the context of
time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...
: what does it mean for something to be itself across two moments in time? How do we account for this? Another question of identity arises when we ask what our criteria ought to be for determining identity, and how the reality of identity interfaces with linguistic expressions. The metaphysical positions one takes on identity have far-reaching implications on issues such as the mind–body problem, personal identity,
ethics Ethics or moral philosophy is a branch of philosophy that "involves systematizing, defending, and recommending concepts of morality, right and wrong action (philosophy), behavior".''Internet Encyclopedia of Philosophy'' The field of ethics, alo ...
, and
law Law is a set of rules that are created and are law enforcement, enforceable by social or governmental institutions to regulate behavior,Robertson, ''Crimes against humanity'', 90. with its precise definition a matter of longstanding debate. ...
. A few ancient Greeks took extreme positions on the nature of change.
Parmenides Parmenides of Elea (; grc-gre, Παρμενίδης ὁ Ἐλεάτης; ) was a pre-Socratic Greek philosopher from Elea in Magna Graecia. Parmenides was born in the Greek colony of Elea, from a wealthy and illustrious family. His date ...
denied change altogether, while
Heraclitus Heraclitus of Ephesus (; grc-gre, wikt:Ἡράκλειτος, Ἡράκλειτος , "Glory of Hera"; ) was an Ancient Greece, ancient Greek Pre-Socratic philosophy, pre-Socratic philosopher from the city of Ephesus, which was then part of th ...
argued that change was ubiquitous: "No man ever steps in the same river twice." Identity, sometimes called numerical identity, is the relation that a thing bears to itself, and which no thing bears to anything other than itself (cf. sameness). A modern philosopher who made a lasting impact on the philosophy of identity was
Leibniz Gottfried Wilhelm (von) Leibniz . ( – 14 November 1716) was a German polymath active as a mathematician, philosopher, scientist and diplomat. He is one of the most prominent figures in both the history of philosophy and the history of mathema ...
, whose ''law of the indiscernibility of identicals'' is still widely accepted today. It states that if some object ''x'' is identical to some object ''y'', then any property that ''x'' has, ''y'' will have as well. Put formally, it states :$\forall x \; \forall y \; \left(x = y \rightarrow \forall P \; \left(P\left(x\right) \leftrightarrow P\left(y\right)\right)\right)$ However, it does seem that objects can change over time. Two rival theories to account for the relationship between change and identity are '' perdurantism'', which treats objects as a series of object-stages, and '' endurantism'', which maintains that the organism—the same object—is present at every stage in its history. By appealing to intrinsic and extrinsic properties, endurantism finds a way to harmonize identity with change. Endurantists believe that objects persist by being strictly numerically identical over time. However, if Leibniz's law of the indiscernibility of identicals is used to define numerical identity here, it seems that objects must be completely unchanged in order to persist. Discriminating between intrinsic properties and extrinsic properties, endurantists state that numerical identity means that, if some object ''x'' is identical to some object ''y'', then any ''intrinsic'' property that ''x'' has, ''y'' will have as well. Thus, if an object persists, ''intrinsic'' properties of it are unchanged, but ''extrinsic'' properties can change over time. Besides the object itself, environments and other objects can change over time; properties that relate to other objects would change even if this object does not change. Perdurantism can harmonize identity with change in another way. In four-dimensionalism, a version of perdurantism, what persists is a four-dimensional object which does not change although three-dimensional slices of the object may differ.

## Space and time

Objects appear to us in space and time, while abstract entities such as classes, properties, and relations do not. How do space and time serve this function as a ground for objects? Are space and time entities themselves, of some form? Must they exist prior to objects? How exactly can they be defined? How is time related to change; must there always be something changing in order for time to exist?

## Causality

Classical philosophy recognized a number of causes, including teleological final causes. In
special relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between Spacetime, space and time. In Albert Einstein's original treatment, the theory is based on two Postulates of ...
and quantum field theory the notions of space, time and causality become tangled together, with temporal orders of causations becoming dependent on who is observing them. The laws of physics are symmetrical in time, so could equally well be used to describe time as running backwards. Why then do we perceive it as flowing in one direction, the arrow of time, and as containing causation flowing in the same direction? For that matter, can an effect precede its cause? This was the title of a 1954 paper by Michael Dummett, which sparked a discussion that continues today. Earlier, in 1947, C. S. Lewis had argued that one can meaningfully pray concerning the outcome of, e.g., a medical test while recognizing that the outcome is determined by past events: "My free act contributes to the cosmic shape." Likewise, some interpretations of
quantum mechanics Quantum mechanics is a fundamental Scientific theory, theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including qua ...
, dating to 1945, involve backward-in-time causal influences.
Causality Causality (also referred to as causation, or cause and effect) is influence by which one event, process, state, or object (''a'' ''cause'') contributes to the production of another event, process, state, or object (an ''effect'') where the ca ...
is linked by many philosophers to the concept of counterfactuals. To say that A caused B means that if A had not happened then B would not have happened. This view was advanced by David Lewis in his 1973 paper "Causation". His subsequent papers further develop his theory of causation. Causality is usually required as a foundation for
philosophy of science Philosophy of science is a branch of philosophy concerned with the foundations, methodology, methods, and implications of science. The central questions of this study concern Demarcation problem, what qualifies as science, the reliability of s ...
if science aims to understand causes and effects and make predictions about them.

## Necessity and possibility

Metaphysicians investigate questions about the ways the world could have been. David Lewis, in '' On the Plurality of Worlds'', endorsed a view called concrete modal realism, according to which facts about how things could have been are made true by other
concrete Concrete is a composite material composed of fine and coarse construction aggregate, aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after wa ...
worlds in which things are different. Other philosophers, including
Gottfried Leibniz Gottfried Wilhelm (von) Leibniz . ( – 14 November 1716) was a German polymath active as a mathematician, philosopher, scientist and diplomat. He is one of the most prominent figures in both the history of philosophy and the history of mathema ...
, have dealt with the idea of possible worlds as well. A necessary fact is true across all possible worlds. A possible fact is true in some possible world, even if not in the actual world. For example, it is possible that cats could have had two tails, or that any particular apple could have not existed. By contrast, certain propositions seem necessarily true, such as analytic propositions, e.g., "All bachelors are unmarried." The view that any analytic truth is necessary is not universally held among philosophers. A less controversial view is that self-identity is necessary, as it seems fundamentally incoherent to claim that any ''x'' is not identical to itself; this is known as the law of identity, a putative "first principle". Similarly, Aristotle describes the principle of non-contradiction: :It is impossible that the same quality should both belong and not belong to the same thing ... This is the most certain of all principles ... Wherefore they who demonstrate refer to this as an ultimate opinion. For it is by nature the source of all the other axioms.

# Peripheral questions

## Metaphysical cosmology and cosmogony

Metaphysical cosmology is the branch of metaphysics that deals with the
world In its most general sense, the term "world" refers to the totality of entities, to the whole of reality or to everything that is. The nature of the world has been conceptualized differently in different fields. Some conceptions see the worl ...
as the totality of all phenomena in
space Space is the boundless Three-dimensional space, three-dimensional extent in which Physical body, objects and events have relative position (geometry), position and direction (geometry), direction. In classical physics, physical space is often ...
and
time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...
. Historically, it formed a major part of the subject alongside ontology, though its role is more peripheral in contemporary philosophy. It has had a broad scope, and in many cases was founded in religion. The ancient Greeks drew no distinction between this use and their model for the cosmos. However, in modern times it addresses questions about the
Universe The universe is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmology, cosmological description of the development of ...
which are beyond the scope of the physical sciences. It is distinguished from religious cosmology in that it approaches these questions using philosophical methods (e.g.
dialectic Dialectic ( grc-gre, διαλεκτική, ''dialektikḗ''; related to dialogue; german: Dialektik), also known as the dialectical method, is a discourse between two or more people holding different points of view about a subject but wishing ...
s). Cosmogony deals specifically with the origin of the universe. Modern metaphysical cosmology and cosmogony try to address questions such as: * What is the origin of the Universe? What is its first cause? Is its existence necessary? (see
monism Monism attributes oneness or singleness (Greek: μόνος) to a concept e.g., existence. Various kinds of monism can be distinguished: * Priority monism states that all existing things go back to a source that is distinct from them; e.g., i ...
,
pantheism Pantheism is the belief that reality, the universe and the cosmos are identical with divinity and a supreme supernatural being or entity, pointing to the universe as being an immanent creator deity A creator deity or creator god (often ...
, emanationism and
creationism Creationism is the religious belief that nature, and aspects such as the universe, Earth, life, and humans, originated with supernatural acts of Creation myth, divine creation.#Gunn 2004, Gunn 2004, p. 9, "The ''Concise Oxford Dictionary'' say ...
) * What are the ultimate material components of the Universe? (see
mechanism Mechanism may refer to: *Mechanism (engineering), rigid bodies connected by joints in order to accomplish a desired force and/or motion transmission *Mechanism (biology), explaining how a feature is created *Mechanism (philosophy), a theory that a ...
, dynamism, hylomorphism,
atomism Atomism (from Ancient Greek, Greek , ''atomon'', i.e. "uncuttable, indivisible") is a natural philosophy proposing that the physical universe is composed of fundamental indivisible components known as atoms. References to the concept of atomism ...
) * What is the ultimate reason for the existence of the Universe? Does the cosmos have a purpose? (see teleology)

## Mind and matter

Accounting for the existence of
mind The mind is the set of faculties responsible for all mental Phenomenon, phenomena. Often the term is also identified with the phenomena themselves. These faculties include thought, imagination, memory, Will (philosophy), will, and Sensation (psy ...
in a world largely composed of
matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic partic ...
is a metaphysical problem which is so large and important as to have become a specialized subject of study in its own right, philosophy of mind. Substance dualism is a classical theory in which mind and body are essentially different, with the mind having some of the attributes traditionally assigned to the
soul In many religious and philosophical traditions, there is a belief that a soul is "the immaterial aspect or essence of a human being". Etymology The Modern English noun '':wikt:soul, soul'' is derived from Old English ''sāwol, sāwel''. The ea ...
, and which creates an immediate conceptual puzzle about how the two interact. This form of substance dualism differs from the dualism of some eastern philosophical traditions (like Nyāya), which also posit a soul; for the soul, under their view, is ontologically distinct from the mind. Idealism postulates that material objects do not exist unless perceived and only as perceptions. Adherents of panpsychism, a kind of property dualism, hold that everything ''has'' a mental aspect, but not that everything exists ''in'' a mind. Neutral monism postulates that existence consists of a single substance that in itself is neither mental nor physical, but is capable of mental and physical aspects or attributesthus it implies a dual-aspect theory. For the last century, the dominant theories have been science-inspired including materialistic monism, type identity theory, token identity theory, functionalism, reductive physicalism, nonreductive physicalism, eliminative materialism, anomalous monism, property dualism, epiphenomenalism and emergentism.

## Determinism and free will

Determinism is the philosophical
proposition In logic and linguistics, a proposition is the meaning of a declarative sentence (linguistics), sentence. In philosophy, "Meaning (philosophy), meaning" is understood to be a non-linguistic entity which is shared by all sentences with the same me ...
that every event, including human cognition, decision and action, is causally determined by an unbroken chain of prior occurrences. It holds that nothing happens that has not already been determined. The principal consequence of the deterministic claim is that it poses a challenge to the existence of free will. The problem of free will is the problem of whether rational agents exercise control over their own actions and decisions. Addressing this problem requires understanding the relation between freedom and causation, and determining whether the laws of nature are causally deterministic. Some philosophers, known as incompatibilists, view determinism and free will as mutually exclusive. If they believe in determinism, they will therefore believe free will to be an illusion, a position known as ''hard determinism''. Proponents range from
Baruch Spinoza Baruch (de) Spinoza (born Bento de Espinosa; later as an author and a correspondent ''Benedictus de Spinoza'', anglicized to ''Benedict de Spinoza''; 24 November 1632 – 21 February 1677) was a Dutch Republic, Dutch philosopher of Spanish and ...
to Ted Honderich. Henri Bergson defended free will in his dissertation '' Time and Free Will'' from 1889. Others, labeled compatibilists (or "soft determinists"), believe that the two ideas can be reconciled coherently. Adherents of this view include
Thomas Hobbes Thomas Hobbes ( ; 5/15 April 1588 – 4/14 December 1679) was an English people, English philosopher, considered to be one of the founders of modern political philosophy. Hobbes is best known for his 1651 book ''Leviathan (Hobbes book), Levi ...
and many modern philosophers such as John Martin Fischer, Gary Watson, Harry Frankfurt, and the like. Incompatibilists who accept free will but reject determinism are called libertarians, a term not to be confused with the political sense. Robert Kane and Alvin Plantinga are modern defenders of this theory.

## Natural and social kinds

The earliest type of classification of social construction traces back to
Plato Plato ( ; grc-gre, wikt:Πλάτων, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greeks, Greek philosopher born in Athens during the Classical Greece, Classical period in Ancient Greece. He founded the Platonist school of thou ...
in his dialogue Phaedrus where he claims that the biological classification system seems to carve nature at the joints. In contrast, later philosophers such as Michel Foucault and Jorge Luis Borges have challenged the capacity of natural and social classification. In his essay The Analytical Language of John Wilkins, Borges makes us imagine a certain encyclopedia where the animals are divided into (a) those that belong to the emperor; (b) embalmed ones; (c) those that are trained; ... and so forth, in order to bring forward the ambiguity of natural and social kinds. According to metaphysics author Alyssa Ney: "The reason all this is interesting is that there seems to be a metaphysical difference between the Borgesian system and Plato's". The difference is not obvious but one classification attempts to carve entities up according to objective distinction while the other does not. According to Quine this notion is closely related to the notion of similarity. The philosopher of social science Jason Josephson Storm has attempted to provide a more precise definition of social kinds, arguing that social kinds may still be real insofar as they are determined by empricially observable causal processes and that many cases of what appear to be natural kinds — including biological natural kinds and the category of "natural kind" itself — are in fact social kinds; such a view would mitigate the need to prioritize natural kinds above social kinds for much scientific practice.

## Number

There are different ways to set up the notion of number in metaphysics theories. Platonist theories postulate number as a fundamental category itself. Others consider it to be a property of an entity called a "group" comprising other entities; or to be a relation held between several groups of entities, such as "the number four is the set of all sets of four things". Many of the debates around universals are applied to the study of number, and are of particular importance due to its status as a foundation for the philosophy of mathematics and for
mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
itself.

## Applied metaphysics

Although metaphysics as a philosophical enterprise is highly hypothetical, it also has practical application in most other branches of philosophy, science, and now also information technology. Such areas generally assume some basic ontology (such as a system of objects, properties, classes, and space-time) as well as other metaphysical stances on topics such as causality and agency, then build their own particular theories upon these. In
science Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earli ...
, for example, some theories are based on the ontological assumption of objects with properties (such as electrons having charge) while others may reject objects completely (such as quantum field theories, where spread-out "electronness" becomes property of space-time rather than an object). "Social" branches of philosophy such as philosophy of morality,
aesthetics Aesthetics, or esthetics, is a branch of philosophy that deals with the nature of beauty and taste (sociology), taste, as well as the philosophy of art (its own area of philosophy that comes out of aesthetics). It examines aesthetic values, ...
and
philosophy of religion Philosophy of religion is "the philosophical examination of the central themes and concepts involved in religious traditions". Philosophical discussions on such topics date from ancient times, and appear in the earliest known texts concerning p ...
(which in turn give rise to practical subjects such as ethics, politics, law, and art) all require metaphysical foundations, which may be considered as branches or applications of metaphysics. For example, they may postulate the existence of basic entities such as value, beauty, and God. Then they use these postulates to make their own arguments about consequences resulting from them. When philosophers in these subjects make their foundations they are doing applied metaphysics, and may draw upon its core topics and methods to guide them, including ontology and other core and peripheral topics. As in science, the foundations chosen will in turn depend on the underlying ontology used, so philosophers in these subjects may have to dig right down to the ontological layer of metaphysics to find what is possible for their theories. Systems engineering is essentially based on metaphysics, although without acknowledging it. This is because systems-engineering is primarily concerned with identifying what would be of interest in a prospective new system. Investigating the nature of the situation aka ontology and surveying the possibilities in measuring, evaluating, specifying, planning, implementing, integrating, testing and using it aka
epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Epis ...
.

# Relation to other disciplines

## Science

Prior to the modern history of science, scientific questions were addressed as a part of
natural philosophy Natural philosophy or philosophy of nature (from Latin ''philosophia naturalis'') is the philosophy, philosophical study of Physics (Aristotle), physics, that is, nature and the physical universe. It was dominant before the development of mode ...
. Originally, the term "science" ( la, scientia) simply meant "knowledge". The
scientific method The scientific method is an Empirical evidence, empirical method for acquiring knowledge that has characterized the development of science since at least the 17th century (with notable practitioners in previous centuries; see the article hist ...
, however, transformed natural philosophy into an
empirical Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...
activity deriving from
experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs wh ...
, unlike the rest of philosophy. By the end of the 18th century, it had begun to be called "science" to distinguish it from other branches of philosophy. Science and philosophy have been considered separated disciplines ever since. Thereafter, metaphysics denoted philosophical enquiry of a non-empirical character into the nature of existence.Peter Gay, ''The Enlightenment'', vol. 1 (''The Rise of Modern Paganism''), Chapter 3, Section II, pp. 132–141. Metaphysics continues asking "why" where science leaves off. For example, any theory of fundamental physics is based on some set of
axiom An axiom, postulate, or assumption is a statement (logic), statement that is taken to be truth, true, to serve as a premise or starting point for further reasoning and arguments. The word comes from the Ancient Greek word (), meaning 'that whi ...
s, which may postulate the existence of entities such as atoms, particles, forces, charges, mass, or fields. Stating such postulates is considered to be the "end" of a science theory. Metaphysics takes these postulates and explores what they mean as human concepts. For example, do all theories of physics require the existence of space and time, objects, and properties? Or can they be expressed using only objects, or only properties? Do the objects have to retain their identity over time or can they change? If they change, then are they still the same object? Can theories be reformulated by converting properties or predicates (such as "red") into entities (such as redness or redness fields) or processes ('there is some redding happening over there' appears in some human languages in place of the use of properties). Is the distinction between objects and properties fundamental to the physical world or to our perception of it? Much recent work has been devoted to analyzing the role of metaphysics in scientific theorizing. Alexandre Koyré led this movement, declaring in his book ''Metaphysics and Measurement'', "It is not by following experiment, but by outstripping experiment, that the scientific mind makes progress." That metaphysical propositions can influence scientific theorizing is John Watkins' most lasting contribution to philosophy. Since 1957 "he showed the ways in which some un-testable and hence, according to Popperian ideas, non-empirical propositions can nevertheless be influential in the development of properly testable and hence scientific theories. These profound results in applied elementary logic...represented an important corrective to positivist teachings about the meaninglessness of metaphysics and of normative claims". Imre Lakatos maintained that all scientific theories have a metaphysical "hard core" essential for the generation of hypotheses and theoretical assumptions. Thus, according to Lakatos, "scientific changes are connected with vast cataclysmic metaphysical revolutions." An example from biology of Lakatos' thesis: David Hull has argued that changes in the ontological status of the species concept have been central in the development of biological thought from
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical Greece, Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatet ...
through Cuvier, Lamarck, and Darwin. Darwin's ignorance of metaphysics made it more difficult for him to respond to his critics because he could not readily grasp the ways in which their underlying metaphysical views differed from his own. In physics, new metaphysical ideas have arisen in connection with
quantum mechanics Quantum mechanics is a fundamental Scientific theory, theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including qua ...
, where subatomic particles arguably do not have the same sort of individuality as the particulars with which philosophy has traditionally been concerned. Also, adherence to a deterministic metaphysics in the face of the challenge posed by the quantum-mechanical
uncertainty principle In quantum mechanics, the uncertainty principle (also known as Heisenberg's uncertainty principle) is any of a variety of Inequality (mathematics), mathematical inequalities asserting a fundamental limit to the accuracy with which the values fo ...
led physicists such as Albert Einstein to propose alternative theories that retained determinism. A.N. Whitehead is famous for creating a process philosophy metaphysics inspired by electromagnetism and special relativity. In chemistry, Gilbert Newton Lewis addressed the nature of motion, arguing that an electron should not be said to move when it has none of the properties of motion. Katherine Hawley notes that the metaphysics even of a widely accepted scientific theory may be challenged if it can be argued that the metaphysical presuppositions of the theory make no contribution to its predictive success.

## Theology

There is a relationship between theological doctrines and philosophical reflection in the philosophy of a religion (such as
Christian philosophy Christian philosophy includes all philosophy carried out by Christians, or in relation to the religion of Christianity. Christian philosophy emerged with the aim of reconciling science and faith, starting from natural rational explanations wit ...
); philosophical reflections are strictly rational. On this way of seeing the two disciplines, if at least one of the premises of an argument is derived from revelation, the argument falls in the domain of theology; otherwise it falls into philosophy's domain.

# Rejections of metaphysics

Meta-metaphysics is the branch of philosophy that is concerned with the foundations of metaphysics. A number of individuals have suggested that much or all of metaphysics should be rejected, a meta-metaphysical position known as metaphysical deflationism or ontological deflationism. In the 16th century,
Francis Bacon Francis Bacon, 1st Viscount St Alban (; 22 January 1561 – 9 April 1626), also known as Lord Verulam, was an English philosopher and statesman who served as Attorney General and Lord Chancellor of England England is a Countries of ...
rejected scholastic metaphysics, and argued strongly for what is now called
empiricism In philosophy, empiricism is an Epistemology, epistemological theory that holds that knowledge or justification comes only or primarily from Empirical evidence, sensory experience. It is one of several views within epistemology, along with ra ...
, being seen later as the father of modern empirical science. In the 18th century, David Hume took a strong position, arguing that all genuine knowledge involves either mathematics or matters of fact and that metaphysics, which goes beyond these, is worthless. He concluded his '' Enquiry Concerning Human Understanding'' (1748) with the statement:
If we take in our hand any volume ook of divinity or school metaphysics, for instance; let us ask, ''Does it contain any abstract reasoning concerning quantity or number?'' No. ''Does it contain any experimental reasoning concerning matter of fact and existence?'' No. Commit it then to the flames: for it can contain nothing but sophistry and illusion.
Thirty-three years after Hume's ''Enquiry'' appeared, Immanuel Kant published his '' Critique of Pure Reason''. Although he followed Hume in rejecting much of previous metaphysics, he argued that there was still room for some synthetic '' a priori'' knowledge, concerned with matters of fact yet obtainable independent of experience. These included fundamental structures of space, time, and causality. He also argued for the freedom of the will and the existence of "things in themselves", the ultimate (but unknowable) objects of experience. Wittgenstein introduced the concept that metaphysics could be influenced by theories of aesthetics, via
logic Logic is the study of correct reasoning. It includes both Mathematical logic, formal and informal logic. Formal logic is the science of Validity (logic), deductively valid inferences or of logical truths. It is a formal science investigating h ...
, vis. a world composed of "atomical facts". In the 1930s, A.J. Ayer and
Rudolf Carnap Rudolf Carnap (; ; 18 May 1891 – 14 September 1970) was a German-language philosopher who was active in Europe before 1935 and in the United States thereafter. He was a major member of the Vienna Circle and an advocate of logical positivism. He ...
endorsed Hume's position; Carnap quoted the passage above. They argued that metaphysical statements are neither true nor false but meaningless since, according to their verifiability theory of meaning, a statement is meaningful only if there can be empirical evidence for or against it. Thus, while Ayer rejected the monism of Spinoza, he avoided a commitment to pluralism, the contrary position, by holding both views to be without meaning. Carnap took a similar line with the controversy over the reality of the external world. While the logical positivism movement is now considered dead (with Ayer, a major proponent, admitting in a 1979 TV interview that "nearly all of it was false"),Oswald Hanfling, Ch. 5 "Logical positivism", in Stuart G Shanker, ''Philosophy of Science, Logic and Mathematics in the Twentieth Century'' (London:
Routledge Routledge () is a British multinational publisher. It was founded in 1836 by George Routledge, and specialises in providing academic books, journals and online resources in the fields of the humanities, behavioural science, education ...
, 1996), pp
193–194
it has continued to influence philosophy development. Arguing against such rejections, the Scholastic philosopher Edward Feser held that Hume's critique of metaphysics, and specifically Hume's fork, is "notoriously self-refuting". Feser argues that Hume's fork itself is not a conceptual truth and is not empirically testable. Some living philosophers, such as Amie Thomasson, have argued that many metaphysical questions can be dissolved just by looking at the way words are used; others, such as Ted Sider, have argued that metaphysical questions are substantive, and that progress can be made toward answering them by comparing theories according to a range of theoretical virtues inspired by the sciences, such as simplicity and explanatory power.

# History and schools of metaphysics

## Pre-history

Cognitive archeology such as analysis of cave paintings and other pre-historic art and customs suggests that a form of
perennial philosophy The perennial philosophy ( la, philosophia perennis), also referred to as perennialism and perennial wisdom, is a perspective in philosophy and spirituality that views all of the world's religious traditions as sharing a single, metaphysical trut ...
or Shamanic metaphysics may stretch back to the birth of behavioral modernity, all around the world. Similar beliefs are found in present-day "stone age" cultures such as Australian aboriginals. Perennial philosophy postulates the existence of a spirit or concept world alongside the day-to-day world, and interactions between these worlds during dreaming and ritual, or on special days or at special places. It has been argued that perennial philosophy formed the basis for Platonism, with Plato articulating, rather than creating, much older widespread beliefs.

## Bronze Age

Bronze Age cultures such as
ancient Mesopotamia The history of Mesopotamia ranges from the earliest human occupation in the Paleolithic period up to Late antiquity. This history is pieced together from evidence retrieved from archaeological excavations and, after the introduction of writing i ...
and
ancient Egypt Ancient Egypt was a civilization in Northeast Africa situated in the Nile Valley. Ancient Egyptian civilization followed prehistoric Egypt and coalesced around 3100Anno Domini, BC (according to conventional Egyptian chronology) with the ...
(along with similarly structured but chronologically later cultures such as Mayans and
Aztecs The Aztecs () were a Mesoamerican culture that flourished in central Mexico in the post-classic period from 1300 to 1521. The Aztec people included different Indigenous peoples of Mexico, ethnic groups of central Mexico, particularly those g ...
) developed belief systems based on
mythology Myth is a folklore genre consisting of narratives that play a fundamental role in a society, such as foundational tales or origin myths. Since "myth" is widely used to imply that a story is not objectively true, the identification of a narra ...
, anthropomorphic
gods A deity or god is a supernatural being who is considered divinity, divine or sacred. The ''Oxford Dictionary of English'' defines deity as a God (male deity), god or goddess, or anything revered as divine. C. Scott Littleton defines a deity as " ...
, mind–body dualism, and a spirit world, to explain causes and cosmology. These cultures appear to have been interested in
astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
and may have associated or identified the stars with some of these entities. In ancient Egypt, the ontological distinction between order ( maat) and chaos ( Isfet) seems to have been important.

## Pre-Socratic Greece

The first named Greek philosopher, according to
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical Greece, Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatet ...
, is Thales of
Miletus Miletus (; gr, Μῑ́λητος, Mī́lētos; Hittite language, Hittite transcription ''Millawanda'' or ''Milawata'' (Exonym and endonym, exonyms); la, Mīlētus; tr, Milet) was an Ancient Greece, ancient Greek city on the western coast of ...
, early 6th century BCE. He made use of purely physical explanations to explain the phenomena of the world rather than the mythological and divine explanations of tradition. He is thought to have posited water as the single underlying principle (or '' arche'' in later Aristotelian terminology) of the material world. His fellow, but younger Miletians,
Anaximander Anaximander (; grc-gre, Ἀναξίμανδρος ''Anaximandros''; ) was a Pre-Socratic philosophy, pre-Socratic Ancient Greek philosophy, Greek philosopher who lived in Miletus,"Anaximander" in ''Chambers's Encyclopædia''. London: George Newn ...
and Anaximenes, also posited monistic underlying principles, namely '' apeiron'' (the indefinite or boundless) and air respectively. Another school was the Eleatics, in southern
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the Italy (geographical region) ...
. The group was founded in the early fifth century BCE by
Parmenides Parmenides of Elea (; grc-gre, Παρμενίδης ὁ Ἐλεάτης; ) was a pre-Socratic Greek philosopher from Elea in Magna Graecia. Parmenides was born in the Greek colony of Elea, from a wealthy and illustrious family. His date ...
, and included
Zeno of Elea Zeno of Elea (; grc, wikt:Ζήνων, Ζήνων ὁ Ἐλεᾱ́της; ) was a pre-Socratic Greek philosopher of Magna Graecia and a member of the Eleatic School founded by Parmenides. Aristotle called him the inventor of the dialectic. He i ...
and
Melissus of Samos Melissus of Samos (; grc, Μέλισσος ὁ Σάμιος; ) was the third and last member of the ancient school of Eleatics, Eleatic philosophy, whose other members included Zeno of Elea, Zeno and Parmenides. Little is known about his life, ex ...
. Methodologically, the Eleatics were broadly rationalist, and took logical standards of clarity and necessity to be the criteria of
truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherwise correspond to it, such as beliefs, ...
. Parmenides' chief doctrine was that reality is a single unchanging and universal Being. Zeno used '' reductio ad absurdum'', to demonstrate the illusory nature of change and time in his
paradoxes A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically u ...
.
Heraclitus Heraclitus of Ephesus (; grc-gre, wikt:Ἡράκλειτος, Ἡράκλειτος , "Glory of Hera"; ) was an Ancient Greece, ancient Greek Pre-Socratic philosophy, pre-Socratic philosopher from the city of Ephesus, which was then part of th ...
of Ephesus, in contrast, made change central, teaching that "all things flow". His philosophy, expressed in brief aphorisms, is quite cryptic. For instance, he also taught the unity of opposites.
Democritus Democritus (; el, Δημόκριτος, ''Dēmókritos'', meaning "chosen of the people"; – ) was an Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient ...
and his teacher Leucippus, are known for formulating an atomic theory for the cosmos. Barnes (1987). They are considered forerunners of the scientific method.

## Classical China

Metaphysics in
Chinese philosophy Chinese philosophy originates in the Spring and Autumn period () and Warring States period The Warring States period () was an era in History of China#Ancient China, ancient Chinese history characterized by warfare, as wel ...
can be traced back to the earliest Chinese philosophical concepts from the
Zhou dynasty The Zhou dynasty ( ; Old Chinese (Reconstructions of Old Chinese#Baxter–Sagart (2014), B&S): *''tiw'') was a Dynasties in Chinese history, royal dynasty of China that followed the Shang dynasty. Having lasted 789 years, the Zhou dynasty was t ...
such as
Tian ''Tiān'' () is one of the oldest Chinese terms for heaven and a key concept in Chinese mythology, Chinese philosophy, philosophy, and Chinese folk religion, religion. During the Shang dynasty (17th―11th century BCE), the Chinese referred to ...
(Heaven) and
yin and yang Yin and yang ( and ) is a Chinese philosophical concept that describes opposite but interconnected forces. In Chinese cosmology, the universe creates itself out of a primary chaos of material energy, organized into the cycles of yin and ya ...
. The fourth century BCE saw a turn towards cosmogony with the rise of
Taoism Taoism (, ) or Daoism () refers to either a school of Philosophy, philosophical thought (道家; ''daojia'') or to a religion (道教; ''daojiao''), both of which share ideas and concepts of China, Chinese origin and emphasize living in harmo ...
(in the Daodejing and Zhuangzi) and sees the natural world as dynamic and constantly changing processes which spontaneously arise from a single immanent metaphysical source or principle ( Tao).Perkins, Franklin
"Metaphysics in Chinese Philosophy"
, The Stanford Encyclopedia of Philosophy (Winter 2016 Edition), Edward N. Zalta (ed.).
Another philosophical school which arose around this time was the School of Naturalists which saw the ultimate metaphysical principle as the Taiji, the "supreme polarity" composed of the forces of yin and yang which were always in a state of change seeking balance. Another concern of Chinese metaphysics, especially Taoism, is the relationship and nature of being and non-being (''you'' 有 and ''wu'' 無). The Taoists held that the ultimate, the Tao, was also non-being or no-presence. Other important concepts were those of spontaneous generation or natural vitality ( Ziran) and "correlative resonance" ( Ganying). After the fall of the Han dynasty (220 CE), China saw the rise of the Neo-Taoist Xuanxue school. This school was very influential in developing the concepts of later Chinese metaphysics.
Buddhist philosophy Buddhist philosophy refers to the Philosophy, philosophical investigations and systems of inquiry that developed among various schools of Buddhism in India following the parinirvana of The Buddha and later spread throughout Asia. The Buddhist ...
entered China (c. 1st century) and was influenced by the native Chinese metaphysical concepts to develop new theories. The native
Tiantai Tiantai or T'ien-t'ai () is an East Asian Buddhism, East Asian Buddhist school of Mahayana Buddhism, Mahāyāna Buddhism that developed in Sui dynasty, 6th-century China. The school emphasizes the ''Lotus Sutra's'' doctrine of the "One Vehicle ...
and Huayen schools of philosophy maintained and reinterpreted the Indian theories of '' shunyata'' (emptiness, ''kong'' 空) and
Buddha-nature Buddha-nature refers to several related Mahayana Buddhism, Buddhist terms, including ''tathata'' ("suchness") but most notably ''tathāgatagarbha'' and ''buddhadhātu''. ''Tathāgatagarbha'' means "the womb" or "embryo" (''garbha'') of the " ...
(''Fo xing'' 佛性) into the theory of interpenetration of phenomena. Neo-Confucians like Zhang Zai under the influence of other schools developed the concepts of "principle" ( li) and vital energy ('' qi'').

## Classical Greece

### Socrates and Plato

Socrates is known for his
dialectic Dialectic ( grc-gre, διαλεκτική, ''dialektikḗ''; related to dialogue; german: Dialektik), also known as the dialectical method, is a discourse between two or more people holding different points of view about a subject but wishing ...
or questioning approach to philosophy rather than a positive metaphysical doctrine. His pupil,
Plato Plato ( ; grc-gre, wikt:Πλάτων, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greeks, Greek philosopher born in Athens during the Classical Greece, Classical period in Ancient Greece. He founded the Platonist school of thou ...
is famous for his theory of forms (which he places in the mouth of Socrates in his dialogues). Platonic realism (also considered a form of idealism) is considered to be a solution to the problem of universals; i.e., what particular objects have in common is that they share a specific Form which is universal to all others of their respective kind. The theory has a number of other aspects: * Epistemological: knowledge of the Forms is more certain than mere sensory data. * Ethical: The Form of the Good sets an objective standard for morality. * Time and Change: The world of the Forms is eternal and unchanging. Time and change belong only to the lower sensory world. "Time is a moving image of Eternity". * Abstract objects and mathematics: Numbers, geometrical figures, etc., exist mind-independently in the World of Forms. Platonism developed into Neoplatonism, a philosophy with a monotheistic and mystical flavour that survived well into the early Christian era.

### Aristotle

Plato's pupil
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical Greece, Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatet ...
wrote widely on almost every subject, including
metaphysics Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
. His solution to the problem of universals contrasts with Plato's. Whereas Platonic Forms are existentially apparent in the visible world, Aristotelian
essence Essence ( la, essentia) is a polysemic term, used in philosophy and theology as a designation for the property (philosophy), property or set of properties that make an entity or substance theory, substance what it fundamentally is, and which it ...
s dwell in particulars. Potentiality and actuality are principles of a
dichotomy A dichotomy is a partition of a set, partition of a whole (or a set) into two parts (subsets). In other words, this couple of parts must be * jointly exhaustive: everything must belong to one part or the other, and * mutually exclusive: nothing ...
which
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical Greece, Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatet ...
used throughout his philosophical works to analyze motion,
causality Causality (also referred to as causation, or cause and effect) is influence by which one event, process, state, or object (''a'' ''cause'') contributes to the production of another event, process, state, or object (an ''effect'') where the ca ...
and other issues. The Aristotelian theory of change and causality stretches to four causes: the material, formal, efficient and final. The efficient cause corresponds to what is now known as a cause ''simplicity''. Final causes are explicitly teleological, a concept now regarded as controversial in science. The Matter/Form dichotomy was to become highly influential in later philosophy as the substance/essence distinction. The opening arguments in Aristotle's ''Metaphysics'', Book I, revolve around the senses, knowledge, experience, theory, and wisdom. The first main focus in the ''Metaphysics'' is attempting to determine how intellect "advances from sensation through memory, experience, and art, to theoretical knowledge". Aristotle claims that eyesight provides the capability to recognize and remember experiences, while sound allows learning.

## Classical India

''More on Indian philosophy:
Hindu philosophy Hindu philosophy encompasses the philosophies, world views and teachings of Hinduism that emerged in History of India, Ancient India which include six systems (''darśana, shad-darśana'') – Samkhya, Yoga (philosophy), Yoga, Nyaya, Vaisheshi ...
''

### Sāṃkhya

''Sāṃkhya'' is an ancient system of Indian philosophy based on a dualism involving the ultimate principles of consciousness and matter. It is described as the rationalist school of
Indian philosophy Indian philosophy refers to philosophical traditions of the Indian subcontinent. A traditional Hindu classification divides āstika and nāstika schools of philosophy, depending on one of three alternate criteria: whether it believes the Ve ...
. It is most related to the
Yoga Yoga (; sa, योग, lit=yoke' or 'union ) is a group of Asana, physical, mental, and Spirituality#Asian traditions, spiritual practices or disciplines which originated in History of India, ancient India and aim to control (yoke) and Ś ...
school of
Hinduism Hinduism () is an Indian religions, Indian religion or ''dharma'', a religious and universal order or way of life by which followers abide. As a religion, it is the Major religious groups, world's third-largest, with over 1.2–1.35 billion ...
, and its method was most influential on the development of Early Buddhism.Roy Perrett, Indian Ethics: Classical traditions and contemporary challenges, Volume 1 (Editor: P Bilimoria et al.), Ashgate, , pp. 149–158 The Sāmkhya is an enumerationist philosophy whose
epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Epis ...
accepts three of six
pramana ''Pramana'' (Sanskrit: प्रमाण, ) literally means "Proof (truth), proof" and "means of knowledge".dualist. Sāmkhya philosophy regards the universe as consisting of two realities; puruṣa (consciousness) and prakṛti (matter). Jiva (a living being) is that state in which puruṣa is bonded to prakṛti in some form. This fusion, state the Samkhya scholars, led to the emergence of ''buddhi'' ("spiritual awareness") and ''ahaṅkāra'' (ego consciousness). The universe is described by this school as one created by purusa-prakṛti entities infused with various permutations and combinations of variously enumerated elements, senses, feelings, activity and mind.Samkhya – Hinduism
Encyclopædia Britannica (2014)
During the state of imbalance, one of more constituents overwhelm the others, creating a form of bondage, particularly of the mind. The end of this imbalance, bondage is called liberation, or
moksha ''Moksha'' (; sa, मोक्ष, '), also called ''vimoksha'', ''vimukti'' and ''mukti'', is a term in Hinduism, Buddhism, Jainism and Sikhism for various forms of emancipation, enlightenment, liberation, and release. In its soteriology, ...
, by the Samkhya school. Gerald James Larson (2011), Classical Sāṃkhya: An Interpretation of Its History and Meaning, Motilal Banarsidass, , pp. 36–47 The existence of God or supreme being is not directly asserted, nor considered relevant by the Samkhya philosophers. Sāṃkhya denies the final cause of Ishvara (God). While the Samkhya school considers the
Vedas FIle:Atharva-Veda samhita page 471 illustration.png, upright=1.2, The Vedas are ancient Sanskrit texts of Hinduism. Above: A page from the ''Atharvaveda''. The Vedas (, , ) are a large body of religious texts originating in ancient India. Co ...
as a reliable source of knowledge, it is an atheistic philosophy according to Paul Deussen and other scholars.Lloyd Pflueger, Person Purity and Power in Yogasutra, in Theory and Practice of Yoga (Editor: Knut Jacobsen), Motilal Banarsidass, , pp. 38–39 A key difference between Samkhya and Yoga schools, state scholars, is that Yoga school accepts a "personal, yet essentially inactive, deity" or "personal god". Samkhya is known for its theory of guṇas (qualities, innate tendencies). Guṇa, it states, are of three types: ''sattva'' being good, compassionate, illuminating, positive, and constructive; ''rajas'' is one of activity, chaotic, passion, impulsive, potentially good or bad; and ''tamas'' being the quality of darkness, ignorance, destructive, lethargic, negative. Everything, all life forms and human beings, state Samkhya scholars, have these three guṇas, but in different proportions. The interplay of these guṇas defines the character of someone or something, of nature and determines the progress of life.James G. Lochtefeld, Guna, in The Illustrated Encyclopedia of Hinduism: A–M, Vol. 1, Rosen Publishing, , p. 265 The Samkhya theory of guṇas was widely discussed, developed and refined by various schools of Indian philosophies, including Buddhism. Samkhya's philosophical treatises also influenced the development of various theories of Hindu ethics.

### Vedānta

Realization of the nature of self-identity is the principal object of the Vedanta system of Indian metaphysics. In the
Upanishad The Upanishads (; sa, उपनिषद् ) are late Vedic Sanskrit texts that supplied the basis of later Hindu philosophy.Wendy Doniger (1990), ''Textual Sources for the Study of Hinduism'', 1st Edition, University of Chicago Press, , ...
s, self-consciousness is not the first-person indexical self-awareness or the self-awareness which is self-reference without identification, and also not the self-consciousness which as a kind of desire is satisfied by another self-consciousness. It is self-realisation; the realisation of the self consisting of consciousness that leads all else. The word ''self-consciousness'' in the Upanishads means the knowledge about the existence and nature of ''manusya'', human being. It means the consciousness of our own real being, the primary reality. Self-consciousness means self-knowledge, the knowledge of Prajna i.e. of Prana which is attained by a Brahman. According to the Upanishads the Atman or Paramatman is phenomenally unknowable; it is the object of realisation. The Atman is unknowable in its essential nature; it is unknowable in its essential nature because it is the eternal subject who knows about everything including itself. The Atman is the knower and also the known. Metaphysicians regard the self either to be distinct from the absolute or entirely identical with the absolute. They have given form to three schools of thought – the ''dualistic school'', the ''quasi-dualistic school'' and the ''monistic school'', as the result of their varying mystical experiences. Prakrti and Atman, when treated as two separate and distinct aspects form the basis of the dualism of the Shvetashvatara Upanishad. Quasi-dualism is reflected in the Vaishnavite-monotheism of Ramanuja and the absolute monism, in the teachings of Adi Shankara. Self-consciousness is the fourth state of consciousness or ''Turiya'', the first three being ''Vaisvanara'', '' Taijasa'' and ''Prajna''. These are the four states of individual consciousness. There are three distinct stages leading to self-realisation. The first stage is in mystically apprehending the glory of the self within one as though one were distinct from it. The second stage is in identifying the "I-within" with the self, that one is in essential nature entirely identical with the pure self. The third stage is in realising that the Atman is Brahman, that there is no difference between the self and the absolute. The fourth stage is in realising "I am the Absolute" – '' Aham Brahman Asmi''. The fifth stage is in realising that Brahman is the "all" that exists, as also that which does not exist.

## Buddhist metaphysics

In
Buddhist philosophy Buddhist philosophy refers to the Philosophy, philosophical investigations and systems of inquiry that developed among various schools of Buddhism in India following the parinirvana of The Buddha and later spread throughout Asia. The Buddhist ...
there are various metaphysical traditions that have proposed different questions about the nature of reality based on the teachings of the Buddha in the early Buddhist texts. The
Buddha Siddhartha Gautama, most commonly referred to as the Buddha, was a śramaṇa, wandering ascetic and religious teacher who lived in South Asia during the 6th or 5th century BCE and founded Buddhism. According to Buddhist tradition, he was ...
of the early texts does not focus on metaphysical questions but on ethical and spiritual training and in some cases, he dismisses certain metaphysical questions as unhelpful and indeterminate Avyakta, which he recommends should be set aside. The development of systematic metaphysics arose after the Buddha's death with the rise of the
Abhidharma The Abhidharma are ancient (third century BCE and later) Buddhism, Buddhist texts which contain detailed scholastic presentations of doctrinal material appearing in the Buddhist sutra, ''sutras''. It also refers to the scholastic method itself ...
traditions. The Buddhist Abhidharma schools developed their analysis of reality based on the concept of ''dharmas'' which are the ultimate physical and mental events that makeup experience and their relations to each other. Noa Ronkin has called their approach " phenomenological". Later philosophical traditions include the
Madhyamika Mādhyamaka ("middle way" or "centrism"; ; Tibetic languages, Tibetan: དབུ་མ་པ ; ''dbu ma pa''), otherwise known as Śūnyavāda ("the Śūnyatā, emptiness doctrine") and Niḥsvabhāvavāda ("the no Svabhava, ''svabhāva'' doctr ...
school of Nagarjuna, which further developed the theory of the emptiness ( shunyata) of all phenomena or dharmas which rejects any kind of
substance Substance may refer to: * Matter, anything that has mass and takes up space Chemistry * Chemical substance, a material with a definite chemical composition * Drug substance ** Substance abuse, drug-related healthcare and social policy diagnosis o ...
. This has been interpreted as a form of anti-foundationalism and anti-realism which sees reality as having no ultimate essence or ground. The
Yogacara Yogachara ( sa, योगाचार, IAST: '; literally "yoga practice"; "one whose practice is yoga") is an influential tradition of Buddhist philosophy and psychology emphasizing the study of cognition, perception, and consciousness through t ...
school meanwhile promoted a theory called "awareness only" ( vijnapti-matra) which has been interpreted as a form of Idealism or Phenomenology and denies the split between awareness itself and the objects of awareness.

## Islamic metaphysics

Major ideas in Islamic metaphysics () have surrounded the concept of ''weḥdah'' (وحدة) meaning 'unity', or in Arabic توحيد ''tawhid''. ''Waḥdat al-wujūd'' literally means the 'unity of existence' or 'unity of being'. In modern times the phrase has been translated as "
pantheism Pantheism is the belief that reality, the universe and the cosmos are identical with divinity and a supreme supernatural being or entity, pointing to the universe as being an immanent creator deity A creator deity or creator god (often ...
." ''Wujud'' (i.e. existence or presence) here refers to Allah's ''wujud'' (compare ''tawhid''). However, ''waḥdat ash-shuhūd'', meaning 'apparentism' or 'monotheism of witness', holds that god and his creation are entirely separate.

## Scholasticism and the Middle Ages

Between about 1100 and 1500, philosophy as a discipline took place as part of the
Catholic church The Catholic Church, also known as the Roman Catholic Church, is the List of Christian denominations by number of members, largest Christian church, with 1.3 billion baptized Catholics Catholic Church by country, worldwide . It is am ...
's teaching system, known as
scholasticism Scholasticism was a medieval school of philosophy that employed a Organon, critical organic method of philosophical analysis predicated upon the Aristotelianism, Aristotelian categories (Aristotle), 10 Categories. Christian scholasticism eme ...
. Scholastic philosophy took place within an established framework blending Christian theology with Aristotelian teachings. Although fundamental orthodoxies were not commonly challenged, there were nonetheless deep metaphysical disagreements, particularly over the problem of universals, which engaged Duns Scotus and Pierre Abelard. William of Ockham is remembered for his principle of ontological parsimony.

## Continental rationalism

In the early modern period (17th and 18th centuries), the system-building ''scope'' of philosophy is often linked to the rationalist ''method'' of philosophy, that is the technique of deducing the nature of the world by pure reason. The scholastic concepts of substance and accident were employed. *
Leibniz Gottfried Wilhelm (von) Leibniz . ( – 14 November 1716) was a German polymath active as a mathematician, philosopher, scientist and diplomat. He is one of the most prominent figures in both the history of philosophy and the history of mathema ...
proposed in his '' Monadology'' a plurality of non-interacting substances. * Descartes is famous for his dualism of material and mental substances. * Spinoza believed reality was a single substance of God-or-nature. Christian Wolff had theoretical philosophy divided into an ontology or ''philosophia prima'' as a general metaphysics, which arises as a preliminary to the distinction of the three " special metaphysics" on the soul, world and God: rational
psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, including feelings and thoughts. It is an academic discipline of immens ...
, rational
cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in ...
and rational theology. The three disciplines are called empirical and rational because they are independent of revelation. This scheme, which is the counterpart of religious tripartition in creature, creation, and Creator, is best known to philosophical students by Kant's treatment of it in the '' Critique of Pure Reason''. In the "Preface" of the 2nd edition of Kant's book, Wolff is defined "the greatest of all dogmatic philosophers."

## British empiricism

British empiricism marked something of a reaction to rationalist and system-building metaphysics, or ''speculative'' metaphysics as it was pejoratively termed. The skeptic
David Hume David Hume (; born David Home; 7 May 1711 New Style, NS (26 April 1711 Old Style, OS) – 25 August 1776)Maurice Cranston, Cranston, Maurice, and T. E. Jessop, Thomas Edmund Jessop. 2020 999avid Hume" ''Encyclopædia Britannica''. Retrieve ...
famously declared that most metaphysics should be consigned to the flames (see below). Hume was notorious among his contemporaries as one of the first philosophers to openly doubt religion, but is better known now for his critique of causality.
John Stuart Mill John Stuart Mill (20 May 1806 – 7 May 1873) was an English philosopher, Political economy, political economist, Member of Parliament (United Kingdom), Member of Parliament (MP) and civil servant. One of the most influential thinkers in the ...
, Thomas Reid and
John Locke John Locke (; 29 August 1632 – 28 October 1704) was an English philosopher and physician, widely regarded as one of the most influential of Age of Enlightenment, Enlightenment thinkers and commonly known as the "father of liberalism ...
were less skeptical, embracing a more cautious style of metaphysics based on realism,
common sense ''Common Sense'' is a 47-page pamphlet written by Thomas Paine in 1775–1776 advocating independence from Kingdom of Great Britain, Great Britain to people in the Thirteen Colonies. Writing in clear and persuasive prose, Paine collected variou ...
and science. Other philosophers, notably George Berkeley were led from empiricism to idealistic metaphysics.

## Kant

Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German Philosophy, philosopher and one of the central Age of Enlightenment, Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemolo ...
attempted a grand synthesis and revision of the trends already mentioned: scholastic philosophy, systematic metaphysics, and skeptical empiricism, not to forget the burgeoning science of his day. As did the systems builders, he had an overarching framework in which all questions were to be addressed. Like Hume, who famously woke him from his 'dogmatic slumbers', he was suspicious of metaphysical speculation, and also places much emphasis on the limitations of the human mind. Kant described his shift in metaphysics away from making claims about an objective noumenal world, towards exploring the subjective phenomenal world, as a Copernican Revolution, by analogy to (though opposite in direction to)
Copernicus Nicolaus Copernicus (; pl, Mikołaj Kopernik; gml, Niklas Koppernigk, german: Nikolaus Kopernikus; 19 February 1473 – 24 May 1543) was a Renaissance The Renaissance ( , ) , from , with the same meanings. is a Periodization, ...
' shift from man (the subject) to the sun (an object) at the center of the universe. Kant saw rationalist philosophers as aiming for a kind of metaphysical knowledge he defined as the '' synthetic apriori''—that is knowledge that does not come from the senses (it is a priori) but is nonetheless about reality (synthetic). Inasmuch as it is about reality, it differs from abstract mathematical propositions (which he terms synthetic apriori), and being apriori it is distinct from empirical, scientific knowledge (which he terms synthetic aposteriori). The only synthetic apriori knowledge we can have is of how our minds organise the data of the senses; that organising framework is space and time, which for Kant have no mind-independent existence, but nonetheless operate uniformly in all humans. Apriori knowledge of space and time is all that remains of metaphysics as traditionally conceived. There ''is'' a reality beyond sensory data or phenomena, which he calls the realm of noumena; however, we cannot know it as it is in itself, but only as it appears to us. He allows himself to speculate that the origins of phenomenal God, morality, and free will ''might'' exist in the noumenal realm, but these possibilities have to be set against its basic unknowability for humans. Although he saw himself as having disposed of metaphysics, in a sense, he has generally been regarded in retrospect as having a metaphysics of his own, and as beginning the modern analytical conception of the subject.

## Late modern philosophy

Nineteenth century philosophy was overwhelmingly influenced by Kant and his successors. Schopenhauer, Schelling, Fichte and Hegel all purveyed their own panoramic versions of
German Idealism German idealism was a philosophical movement that emerged in Germany in the late 18th and early 19th centuries. It developed out of the work of Immanuel Kant in the 1780s and 1790s, and was closely linked both with Romanticism and the revolutionary ...
, Kant's own caution about metaphysical speculation, and refutation of idealism, having fallen by the wayside. The idealistic impulse continued into the early twentieth century with British idealists such as F. H. Bradley and J. M. E. McTaggart. Followers of
Karl Marx Karl Heinrich Marx (; 5 May 1818 – 14 March 1883) was a German philosopher, economist, historian, sociologist, political theorist, journalist, Critique of political economy, critic of political economy, and socialist revolutionary. His be ...
took Hegel's dialectic view of history and re-fashioned it as materialism.

## Early analytic philosophy and positivism

During the period when idealism was dominant in philosophy, science had been making great advances. The arrival of a new generation of scientifically minded philosophers led to a sharp decline in the popularity of idealism during the 1920s. Analytic philosophy was spearheaded by Bertrand Russell and G. E. Moore. Russell and William James tried to compromise between idealism and materialism with the theory of neutral monism. The early to mid-twentieth-century philosophy saw a trend to reject metaphysical questions as meaningless. The driving force behind this tendency was the philosophy of
logical positivism Logical positivism, later called logical empiricism, and both of which together are also known as neopositivism, is a movement in Western philosophy whose central thesis was the verification principle (also known as the verifiability criterion ...
as espoused by the Vienna Circle, which argued that the meaning of a statement was its prediction of observable results of an experiment, and thus that there is no need to postulate the existence of any objects other than these perceptual observations. At around the same time, the American pragmatists were steering a middle course between materialism and idealism. System-building metaphysics, with a fresh inspiration from science, was revived by A. N. Whitehead and Charles Hartshorne.

## Continental philosophy

The forces that shaped analytic philosophy—the break with idealism, and the influence of science—were much less significant outside the English speaking world, although there was a shared turn toward language. Continental philosophy continued in a trajectory from post Kantianism. The phenomenology of Husserl and others was intended as a collaborative project for the investigation of the features and structure of consciousness common to all humans, in line with Kant's basing his synthetic apriori on the uniform operation of consciousness. It was officially neutral with regards to ontology, but was nonetheless to spawn a number of metaphysical systems. Brentano's concept of intentionality would become widely influential, including on analytic philosophy. Heidegger, author of '' Being and Time'', saw himself as re-focusing on Being-qua-being, introducing the novel concept of '' Dasein'' in the process. Classing himself an existentialist, Sartre wrote an extensive study of '' Being and Nothingness''. The speculative realism movement marks a return to full blooded realism.

## Process metaphysics

There are two fundamental aspects of everyday experience: change and persistence. Until recently, the Western philosophical tradition has arguably championed substance and persistence, with some notable exceptions, however. According to process thinkers, novelty, flux and accident do matter, and sometimes they constitute the ultimate reality. In a broad sense, process metaphysics is as old as Western philosophy, with figures such as Heraclitus, Plotinus, Duns Scotus, Leibniz, David Hume, Georg Wilhelm Friedrich Hegel, Friedrich Wilhelm Joseph von Schelling, Gustav Theodor Fechner, Friedrich Adolf Trendelenburg, Charles Renouvier, Karl Marx, Ernst Mach, Friedrich Wilhelm Nietzsche, Émile Boutroux, Henri Bergson, Samuel Alexander and Nicolas Berdyaev. It seemingly remains an open question whether major "Continental" figures such as the late Martin Heidegger, Maurice Merleau-Ponty, Gilles Deleuze, Michel Foucault, or Jacques Derrida should be included. In a strict sense, process metaphysics may be limited to the works of a few philosophers: G. W. F. Hegel, Charles Sanders Peirce, William James, Henri Bergson, A. N. Whitehead, and John Dewey. From a European perspective, there was a very significant and early Whiteheadian influence on the works of outstanding scholars such as Émile Meyerson (1859–1933), Louis Couturat (1868–1914), Jean Wahl (1888–1974), Robin George Collingwood (1889–1943), Philippe Devaux (1902–1979), Hans Jonas (1903–1993), Dorothy M. Emmett (1904–2000), Maurice Merleau Ponty (1908–1961), Enzo Paci (1911–1976), Charlie Dunbar Broad (1887–1971), Wolfe Mays (1912–2005), Ilya Prigogine (1917–2003), Jules Vuillemin (1920–2001), Jean Ladrière (1921–2007), Gilles Deleuze (1925–1995), Wolfhart Pannenberg (1928–2014), Reiner Wiehl (1929–2010), and Alain Badiou (1937-).

## Contemporary analytic philosophy

While early analytic philosophy tended to reject metaphysical theorizing, under the influence of logical positivism, it was revived in the second half of the twentieth century. Philosophers such as David K. Lewis and David Armstrong developed elaborate theories on a range of topics such as universals, causation, possibility and necessity and abstract objects. However, the focus of analytic philosophy generally is away from the construction of all-encompassing systems and toward close analysis of individual ideas. Among the developments that led to the revival of metaphysical theorizing were Quine's attack on the analytic–synthetic distinction, which was generally taken to undermine Carnap's distinction between existence questions internal to a framework and those external to it. The philosophy of fiction, the problem of empty names, and the debate over existence's status as a property have all come of relative obscurity into the limelight, while perennial issues such as free will, possible worlds, and the philosophy of time have had new life breathed into them.Van Inwagen, Peter, and Dean Zimmerman (eds.) (1998), ''Metaphysics: The Big Questions.'' The analytic view is of metaphysics as studying phenomenal human concepts rather than making claims about the noumenal world, so its style often blurs into
philosophy of language In analytic philosophy, philosophy of language investigates the nature of language and the relations between language, language users, and the world. Investigations may include inquiry into the nature of Meaning (philosophy of language), meanin ...
and introspective psychology. Compared to system-building, it can seem very dry, stylistically similar to computer programming, mathematics or even accountancy (as a common stated goal is to "account for" entities in the world).

* Computational metaphysics * Doctor of Metaphysics * Feminist metaphysics * Fundamental question of metaphysics * Metacognition * Metaphilosophy ** Meta-epistemology ** Meta-ethics ** Meta-ontology ** Metasemantics * Metaphysical fiction novels * Metaphysical grounding *
Philosophical logic Understood in a narrow sense, philosophical logic is the area of logic that studies the application of logical methods to philosophy, philosophical problems, often in the form of extended logical systems like modal logic. Some theorists conceive ph ...
*
Philosophical realism Philosophical realism is usually not treated as a position of its own but as a stance towards other subject matters. Realism about a certain kind of thing (like Mathematical realism, numbers or Moral realism, morality) is the thesis that this kin ...
*
Philosophy of science Philosophy of science is a branch of philosophy concerned with the foundations, methodology, methods, and implications of science. The central questions of this study concern Demarcation problem, what qualifies as science, the reliability of s ...
* Philosophical theology

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* Benovsky, Jiri (2016), ''Meta-metaphysics: On Metaphysical Equivalence, Primitiveness, and Theory Choice''. Springer. * Bliss, Ricki and J. T. M. Miller, eds. (forthcoming). ''The Routledge Handbook of Metametaphysics''. Routledge. * Kim, Jaegwon and Ernest Sosa, eds. (1999). ''Metaphysics: An Anthology''. Blackwell Philosophy Anthologies. * Kim, Jaegwon and Ernest Sosa, eds. (2000). ''A Companion to Metaphysics''. Malden Massachusetts. Blackwell. * Neil A. Manson, Robert W. Barnard, eds. (2014). ''The Bloomsbury Companion to Metaphysics''. Bloomsbury. * Raven, Michael J. (2020). ''The Routledge Handbook of Metaphysical Grounding''. Routledge.