Metaphysics is the branch ofphilosophy that examines the basic structure ofreality. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the conceptual framework of human understanding. Some philosophers, includingAristotle, designate metaphysics asfirst philosophy to suggest that it is more fundamental than other forms of philosophical inquiry.
Metaphysics encompasses a wide range of general and abstract topics. It investigates the nature ofexistence, the features all entities have in common, and their division intocategories of being. An influential division is betweenparticulars anduniversals. Particulars are individual unique entities, like a specific apple. Universals are general features that different particulars have in common, like the colorred.Modal metaphysics examines what it means for something to be possible or necessary. Metaphysicians also explore theconcepts of space, time, and change, and their connection tocausality and thelaws of nature. Other topics include howmind and matter are related, whether everything in the world ispredetermined, and whether there isfree will.
Metaphysicians usevarious methods to conduct their inquiry. Traditionally, they rely on rationalintuitions andabstract reasoning but have recently includedempirical approaches associated with scientific theories. Due to the abstract nature of its topic, metaphysics has received criticisms questioning the reliability of its methods and the meaningfulness of its theories. Metaphysics is relevant to many fields of inquiry that often implicitly rely on metaphysical concepts and assumptions.
The precise nature of metaphysics is disputed and its characterization has changed in the course of history. Some approaches see metaphysics as a unified field and give a wide-sweeping definition by understanding it as the study of "fundamental questions about the nature of reality" or as an inquiry into theessences of things. Another approach doubts that the different areas of metaphysics share a set of underlying features and provides instead a fine-grained characterization by listing all the main topics investigated by metaphysicians.[4] Some definitions are descriptive by providing an account of what metaphysicians do while others are normative and prescribe what metaphysicians ought to do.[5]
Two historically influential definitions inancient andmedieval philosophy understand metaphysics as the science of thefirst causes and as the study of beingqua being, that is, the topic of what all beings have in common and to what fundamental categories they belong. In the modern period, the scope of metaphysics expanded to include topics such as the distinction between mind and body andfree will.[6] Some philosophers followAristotle in describing metaphysics as "first philosophy", suggesting that it is the most basic inquiry upon which all other branches of philosophy depend in some way.[7][b]
Immanuel Kant conceived metaphysics from the perspective ofcritical philosophy as the study of the principles underlying all human thought and experience.
Metaphysics is traditionally understood as a study of mind-independent features of reality. Starting withImmanuel Kant'scritical philosophy, an alternative conception gained prominence that focuses on conceptual schemes rather than external reality. Kant distinguishes transcendent metaphysics, which aims to describe the objective features of reality beyond sense experience, from thecritical perspective on metaphysics, which outlines the aspects and principles underlying all human thought and experience.[9] PhilosopherP. F. Strawson further explored the role of conceptual schemes, contrasting descriptive metaphysics, which articulates conceptual schemes commonly used to understand the world, with revisionary metaphysics, which aims to produce better conceptual schemes.[10]
Metaphysics differs from the individual sciences by studying the most general and abstract aspects of reality. The individual sciences, by contrast, examine more specific and concrete features and restrict themselves to certain classes of entities, such as the focus on physical things inphysics, living entities inbiology, and cultures inanthropology.[11] It is disputed to what extent this contrast is a strict dichotomy rather than a gradual continuum.[12]
The wordmetaphysics has its origin in the ancient Greek wordsmetá (μετά, meaning'after','above', and'beyond') andphusiká (φυσικά), as a short form ofta metá ta phusiká, meaning'what comes after the physics'. This is often interpreted to mean that metaphysics discusses topics that, due to their generality and comprehensiveness, lie beyond the realm of physics and its focus on empirical observation.[13] Metaphysics may have received its name by a historical accident whenAristotle's book on this subject was published.[14] Aristotle did not use the termmetaphysics but his editor (likelyAndronicus of Rhodes) may have coined it for its title to indicate that this book should be studied after Aristotle's book published onphysics: literally'after physics'. The term entered the English language through the Latin wordmetaphysica.[13]
The nature of metaphysics can also be characterized in relation to its main branches. An influential division from earlymodern philosophy distinguishes between general and special or specific metaphysics.[15] General metaphysics, also calledontology,[c] takes the widest perspective and studies the most fundamental aspects of being. It investigates the features that all entities share and how entities can be divided into differentcategories. Categories are the most general kinds, such as substance, property,relation, andfact.[17] Ontologists research which categories there are, how they depend on one another, and how they form a system of categories that provides a comprehensive classification of all entities.[18]
Special metaphysics considers being from more narrow perspectives and is divided into subdisciplines based on the perspective they take.Metaphysical cosmology examines changeable things and investigates how they are connected to form aworld as a totality extending through space and time.[19] Rational psychology focuses on metaphysical foundations and problems concerning the mind, such as its relation to matter and the freedom of the will. Natural theology studies the divine and its role as the first cause.[19] The scope of special metaphysics overlaps with other philosophical disciplines, making it unclear whether a topic belongs to it or to areas likephilosophy of mind andtheology.[20]
Starting in the second half of the 20th century, applied metaphysics was conceived as the area ofapplied philosophy examining the implications and uses of metaphysics, both within philosophy and other fields of inquiry. In areas likeethics andphilosophy of religion, it addresses topics like the ontological foundations of moral claims and religious doctrines.[21] Beyond philosophy, its applications include the use of ontologies inartificial intelligence,economics, andsociology to classify entities.[22] Inpsychiatry andmedicine, it examines the metaphysical status ofdiseases.[23]
Meta-metaphysics[d] is themetatheory of metaphysics and investigates the nature and methods of metaphysics. It examines how metaphysics differs from other philosophical and scientific disciplines and assesses its relevance to them. Even though discussions of these topics have a long history in metaphysics, meta-metaphysics has only recently developed into a systematic field of inquiry.[25]
Metaphysicians often regard existence or being as one of the most basic and general concepts.[26] To exist means to be part ofreality, distinguishing real entities from imaginary ones.[27] According to a traditionally influential view, existence is a property of properties: if an entity exists then its properties are instantiated.[28] A different position states that existence is a property of individuals, meaning that it is similar to other properties, such as shape or size.[29] It is controversial whether all entities have this property. According to philosopherAlexius Meinong, there arenonexistent objects, including merely possible objects likeSanta Claus andPegasus.[30][e] A related question is whether existence is the same for all entities or whether there are different modes or degrees of existence.[31] For instance, Plato held thatPlatonic forms, which are perfect and immutable ideas, have a higher degree of existence than matter, which can only imperfectly reflect Platonic forms.[32][f]
Another key concern in metaphysics is the division of entities into distinct groups based on underlying features they share. Theories of categories provide a system of the most fundamental kinds or the highest genera of being by establishing a comprehensive inventory of everything.[34] One of the earliest theories of categories was proposed by Aristotle, who outlined asystem of 10 categories. He argued thatsubstances (e.g., man and horse), are the most important category since all other categories likequantity (e.g., four),quality (e.g., white), and place (e.g., in Athens) are said of substances and depend on them.[35] Kant understood categories as fundamental principles underlying human understanding and developed asystem of 12 categories, divided into the four classes: quantity, quality, relation, and modality.[36] More recent theories of categories were proposed byC. S. Peirce,Edmund Husserl,Samuel Alexander,Roderick Chisholm, andE. J. Lowe.[37] Many philosophers rely on the contrast betweenconcrete and abstract objects. According to a common view, concrete objects, like rocks, trees, and human beings, exist in space and time, undergo changes, and impact each other as cause and effect. They contrast with abstract objects, likenumbers andsets, which do not exist in space and time, are immutable, and do not engage in causal relations.[38]
Particulars are individual entities and include both concrete objects, like Aristotle, the Eiffel Tower, or a specific apple, and abstract objects, like the number 2 or a specific set in mathematics. They are unique, non-repeatable entities and contrast withuniversals, like the color red, which can at the same time exist in several places and characterize several particulars.[39] A widely held view is that particulars instantiate universals but are not themselves instantiated by something else, meaning that they exist in themselves while universals exist in something else.Substratum theory, associated withJohn Locke's philosophy, analyzes each particular as a substratum, also calledbare particular, together with various properties. The substratum confers individuality to the particular while the properties express its qualitative features or what it is like. This approach is rejected bybundle theorists. Inspired byDavid Hume's philosophy, they state that particulars are only bundles of properties without an underlying substratum. Some bundle theorists include in the bundle an individual essence, calledhaecceity followingscholastic terminology, to ensure that each bundle is unique. Another proposal for concrete particulars is that they are individuated by their space-time location.[40]
Concrete particulars encountered in everyday life, like rocks, tables, and organisms, are complex entitiescomposed of various parts. For example, a table consists of a tabletop and legs, each of which is itself made up of countless particles. The relation between parts and wholes is studied bymereology.[41][g] The problem of the many is a philosophical question about the conditions under which several individual things compose a larger whole. For example, a cloud comprises many droplets without a clear boundary, raising the question of which droplets form part of the cloud. According to mereological universalists, every collection of entities forms a whole. This means that what seems to be a single cloud is an overlay of countless clouds, one for each cloud-like collection of water droplets. Mereological moderatists hold that certain conditions must be met for a group of entities to compose a whole, for example, that the entities touch one another.Mereological nihilists reject the idea of wholes altogether, claiming that there are no clouds or tables but only particles that are arranged cloud-wise or table-wise.[43] A related mereological problem is whether there are simple entities that have no parts, asatomists claim, or whether everything can be endlessly subdivided into smaller parts, as continuum theorists contend.[44]
Universals are general entities, encompassing bothproperties andrelations, that express what particulars are like and how they resemble one another. They are repeatable, meaning that they are not limited to a unique existent but can be instantiated by different particulars at the same time. For example, the particularsNelson Mandela andMahatma Gandhi instantiate the universalhumanity, similar to how a strawberry and a ruby instantiate the universalred.[45]
A topic discussed since ancient philosophy, theproblem of universals consists in the challenge of characterizing the ontological status of universals.[46] Realists argue that universals are real, mind-independent entities that exist in addition to particulars. According toPlatonic realists, universals exist independently of particulars, which implies that the universalred would continue to exist even if there were no red things. A moremoderate form of realism, inspired by Aristotle, states that universals depend on particulars, meaning that they are only real if they are instantiated.Nominalists reject the idea that universals exist in either form. For them, the world is composed exclusively of particulars.Conceptualists offer an intermediate position, stating that universals exist, but only asconcepts in the mind used to order experience by classifying entities.[47][h]
Natural and social kinds are often understood as special types of universals. Entities belonging to the same natural kind share certain fundamental features characteristic of the structure of the natural world. In this regard, natural kinds are not an artificially constructed classification but are discovered,[i] usually by the natural sciences, and include kinds likeelectrons,H2O, and tigers.Scientific realists and anti-realists disagree about whether natural kinds exist.[50] Social kinds, likemoney andbaseball,[51] are studied bysocial metaphysics and characterized as useful social constructions that, while not purely fictional, do not reflect the fundamental structure of mind-independent reality.[52]
The concepts of possibility and necessity convey what can or must be the case, expressed in modal statements like "it is possible to find a cure for cancer" and "it is necessary that two plus two equals four". Modal metaphysics studies metaphysical problems surrounding possibility and necessity, for instance, why some modal statements are true while others are false.[53][j] Some metaphysicians hold that modality is a fundamental aspect of reality, meaning that besides facts about what is the case, there are additional facts about what could or must be the case.[55] A different view argues that modal truths are not about an independent aspect of reality but can be reduced to non-modal characteristics, for example, to facts about what properties or linguistic descriptions are compatible with each other or tofictional statements.[56]
Borrowing a term from German philosopherGottfried Wilhelm Leibniz'stheodicy, many metaphysicians use the concept ofpossible worlds to analyze the meaning and ontological ramifications of modal statements. A possible world is a complete and consistent way the totality of things could have been.[57] For example, thedinosaurs werewiped out in the actual world but there are possible worlds in which they are still alive.[58] According to possible world semantics, a statement is possibly true if it is true in at least one possible world, whereas it is necessarily true if it is true in all possible worlds.[59]Modal realists argue that possible worlds exist as concrete entities in the same sense as the actual world, with the main difference being that the actual world is the world we live in while other possible worlds are inhabited bycounterparts. This view is controversial and various alternatives have been suggested, for example, that possible worlds only exist as abstract objects or are similar to stories told in works offiction.[60]
Space andtime are dimensions that entities occupy. Spacetime realists state that space and time are fundamental aspects of reality and exist independently of the human mind. Spacetime idealists, by contrast, hold that space and time are constructs of the human mind, created to organize and make sense of reality.[61] Spacetime absolutism or substantivalism understands spacetime as a distinct object, with some metaphysicians conceptualizing it as a container that holds all other entities within it.Spacetime relationism sees spacetime not as an object but as a network of relations between objects, such as the spatial relation ofbeing next to and the temporal relation ofcoming before.[62]
In the metaphysics of time, an important contrast is between theA-series and the B-series. According to the A-series theory, theflow of time is real, meaning that events are categorized into the past, present, and future. The present continually moves forward in time and events that are in the present now will eventually change their status and lie in the past. From the perspective of the B-series theory, time is static, and events are ordered by the temporal relations earlier-than and later-than without any essential difference between past, present, and future.[63]Eternalism holds that past, present, and future are equally real, whereaspresentism asserts that only entities in the present exist.[64]
Material objects persist through time and change in the process, like a tree that grows or loses leaves.[65] The main ways of conceptualizing persistence through time areendurantism andperdurantism. According to endurantism, material objects are three-dimensional entities that are wholly present at each moment. As they change, they gain or lose properties but otherwise remain the same. Perdurantists see material objects as four-dimensional entities that extend through time and are made up of differenttemporal parts. At each moment, only one part of the object is present, not the object as a whole. Change means that an earlier part is qualitatively different from a later part. For example, when a banana ripens, there is an unripe part followed by a ripe part.[66]
Causality is the relation between cause and effect whereby one entity produces or alters another entity.[67] For instance, if a person bumps a glass and spills its contents then the bump is the cause and the spill is the effect.[68] Besides the single-case causation between particulars in this example, there is also general-case causation expressed in statements such as "smoking causes cancer".[69] The termagent causation is used when people and their actions cause something.[70] Causation is usually interpreted deterministically, meaning that a cause always brings about its effect. However, some philosophers such asG. E. M. Anscombe have provided counterexamples to this idea.[71] Such counterexamples have inspired the development ofprobabilistic theories, which claim that the cause merely increases the probability that the effect occurs. This view can explain that smoking causes cancer even though this does not happen in every single case.[72]
Theregularity theory of causation, inspired byDavid Hume's philosophy, states that causation is nothing but aconstant conjunction in which the mind apprehends that one phenomenon, like putting one's hand in a fire, is always followed by another phenomenon, like a feeling of pain.[73] According to nomic regularity theories, regularities manifest aslaws of nature studied by science.[74]Counterfactual theories focus not on regularities but on how effects depend on their causes. They state that effects owe their existence to the cause and would not occur without them.[75] According to primitivism, causation is a basic concept that cannot be analyzed in terms of non-causal concepts, such as regularities or dependence relations. One form of primitivism identifies causal powers inherent in entities as the underlying mechanism.[76] Eliminativists reject the above theories by holding that there is no causation.[77]
Different approaches toward resolving the mind–body problem[78]
Mind encompasses phenomena likethinking,perceiving,feeling, anddesiring as well as the underlying faculties responsible for these phenomena.[79] Themind–body problem is the challenge of clarifying the relation between physical and mental phenomena. According toCartesian dualism, minds and bodies are distinct substances. They causally interact with each other in various ways but can, at least in principle, exist on their own.[80] This view is rejected bymonists, who argue that reality is made up of only one kind. According to metaphysicalidealism, everything is mental or dependent on the mind, including physical objects, which may be understood as ideas or perceptions of conscious minds.[k] Materialists, by contrast, state that all reality is at its core material. Some deny that mind exists but the more common approach is to explain mind in terms of certain aspects of matter, such as brain states, behavioraldispositions, or functional roles.[82]Neutral monists argue that reality is fundamentally neither material nor mental and suggest that matter and mind are both derivative phenomena.[83] A key aspect of the mind–body problem is thehard problem of consciousness or how to explain that physical systems like brains can produce phenomenal consciousness.[84]
The status of free will as the ability of a person to choose theiractions is a central aspect of the mind–body problem.[85] Metaphysicians are interested in the relation between free will andcausal determinism—the view that everything in the universe, including human behavior, is determined by preceding events and laws of nature. It is controversial whether causal determinism is true, and, if so, whether this would imply that there is no free will. According toincompatibilism, free will cannot exist in a deterministic world since there is no true choice or control if everything is determined.[l]Hard determinists infer from this that there is no free will, whereaslibertarians conclude that determinism must be false.Compatibilists offer a third perspective, arguing that determinism and free will do not exclude each other, for instance, because a person can still act in tune with their motivation and choices even if they are determined by other forces. Free will plays a key role in ethics regarding themoral responsibility people have for what they do.[87]
Identity is a relation that every entity has to itself as a form of sameness. It refers to numerical identity when the same entity is involved, as in the statement "themorning star is theevening star" (both are the planetVenus). In a slightly different sense, it encompasses qualitative identity, also calledexact similarity andindiscernibility, which occurs when two distinct entities are exactly alike, such as perfect identical twins.[88] The principle of the indiscernibility of identicals is widely accepted and holds that numerically identical entities exactly resemble one another. The converse principle, known as theidentity of indiscernibles or Leibniz's Law, is more controversial and states that two entities are numerically identical if they exactly resemble one another.[89] Another distinction is between synchronic and diachronic identity. Synchronic identity relates an entity to itself at the same time, whereas diachronic identity is about the same entity at different times, as in statements like "the table I bought last year is the same as the table in my dining room now".[90]Personal identity is a related topic in metaphysics that uses the termidentity in a slightly different sense and concerns questions like whatpersonhood is or what makes someone a person.[91]
Various contemporary metaphysicians rely on the concepts oftruth,truth-bearer, andtruthmaker to conduct their inquiry.[92] Truth is a property of being in accord with reality. Truth-bearers are entities that can be true or false, such as linguistic statements and mental representations. A truthmaker of a statement is the entity whose existence makes the statement true.[93] For example, the fact that a tomato exists and that it is red acts as a truthmaker for the statement "a tomato is red".[94] Based on this observation, it is possible to pursue metaphysical research by asking what the truthmakers of statements are, with different areas of metaphysics being dedicated to different types of statements. According to this view, modal metaphysics asks what makes statements about what is possible and necessary true while the metaphysics of time is interested in the truthmakers of temporal statements about the past, present, and future.[95] A closely related topic concerns the nature of truth. Theories of truth aim to determine this nature and includecorrespondence,coherence,pragmatic,semantic, anddeflationary theories.[96]
Metaphysicians employ a variety ofmethods to develop metaphysical theories and formulate arguments for and against them.[97] Traditionally,a priori methods have been the dominant approach. They rely on rationalintuition and abstract reasoning from general principles rather than sensoryexperience.A posteriori approaches, by contrast, ground metaphysical theories inempirical observations and scientific theories.[98] Some metaphysicians incorporate perspectives from fields such asphysics,psychology,linguistics, andhistory into their inquiry.[99] The two approaches are not mutually exclusive: it is possible to combine elements from both.[100] The method a metaphysician chooses often depends on their understanding of the nature of metaphysics, for example, whether they see it as an inquiry into the mind-independent structure of reality, asmetaphysical realists claim, or the principles underlying thought and experience, as somemetaphysical anti-realists contend.[101]
A priori approaches often rely on intuitions—non-inferential impressions about the correctness of specific claims or general principles.[102][m] For example, arguments for theA-theory of time, which states that time flows from the past through the present and into the future, often rely on pre-theoretical intuitions associated with the sense of the passage of time.[105] Some approaches use intuitions to establish a small set ofself-evident fundamental principles, known asaxioms, and employdeductive reasoning to build complex metaphysical systems by drawing conclusions from these axioms.[106] Intuition-based approaches can be combined withthought experiments, which help evoke and clarify intuitions by linking them to imagined situations. They usecounterfactual thinking to assess the possible consequences of these situations.[107] For example, to explore the relation between matter and consciousness, some theorists compare humans tophilosophical zombies—hypothetical creatures identical to humans but withoutconscious experience.[108] A related method relies on commonly accepted beliefs instead of intuitions to formulate arguments and theories. Thecommon-sense approach is often used to criticize metaphysical theories that deviate significantly from how the average person thinks about an issue. For example, common-sense philosophers have argued thatmereological nihilism is false since it implies that commonly accepted things, like tables, do not exist.[109]
Conceptual analysis, a method particularly prominent inanalytic philosophy, aims to decompose metaphysical concepts into component parts to clarify their meaning and identify essential relations.[110] Inphenomenology, the method ofeidetic variation is used to investigate essential structures underlyingphenomena. This method involves imagining an object and varying its features to determine which ones are essential and cannot be changed.[111] Thetranscendental method is a further approach and examines the metaphysical structure of reality by observing what entities there are and studying theconditions of possibility without which these entities could not exist.[112]
Some approaches give less importance toa priori reasoning and view metaphysics as a practice continuous with the empirical sciences that generalizes their insights while making their underlying assumptions explicit. This approach is known asnaturalized metaphysics and is closely associated with the work ofWillard Van Orman Quine.[113] He relies on the idea that true sentences from the sciences and other fields haveontological commitments, that is, they imply that certain entities exist.[114] For example, if the sentence "some electrons are bonded to protons" is true then it can be used to justify that electrons and protons exist.[115] Quine used this insight to argue that one can learn about metaphysics by closely analyzing[n] scientific claims to understand what kind of metaphysical picture of the world they presuppose.[117]
In addition to methods of conducting metaphysical inquiry, there are various methodological principles used to decide between competing theories by comparing their theoretical virtues.Ockham's Razor is a well-known principle that gives preference to simple theories, in particular, those that assume that few entities exist. Other principles considerexplanatory power, theoretical usefulness, and proximity to established beliefs.[118]
David Hume criticizes metaphysicians for trying to gain knowledge outside the field of sensory experience.
Despite its status as one of the main branches of philosophy, metaphysics has received numerous criticisms questioning its legitimacy as a field of inquiry.[119] One criticism argues that metaphysical inquiry is impossible because humans lack the cognitive capacities needed to access the ultimate nature of reality.[120] This line of thought leads toskepticism about the possibility of metaphysical knowledge. Empiricists often follow this idea, like Hume, who asserts that there is no goodsource of metaphysical knowledge since metaphysics lies outside the field ofempirical knowledge and relies on dubious intuitions about the realm beyond sensory experience. Arguing that the mind actively structures experience,Kant criticizes traditional metaphysics for its attempt to gain insight into the mind-independent nature of reality. He asserts that knowledge is limited to the realm of possible experience, meaning that humans are not able to decide questions likewhether the world has a beginning in time or is infinite. A related argument favoring the unreliability of metaphysical theorizing points to the deep and lastingdisagreements about metaphysical issues, suggesting a lack of overall progress.[121]
Another criticism holds that the problem lies not with human cognitive abilities but with metaphysical statements themselves, which some claim are neither true nor false butmeaningless. According tological positivists, for instance, the meaning of a statement is given by the procedure used toverify it, usually through theobservations that would confirm it. Based on this controversial assumption, they argue that metaphysical statements are meaningless since they make no testable predictions about experience.[122]
A slightly weaker position allows metaphysical statements to have meaning while holding that metaphysical disagreements are merely verbal disputes about different ways to describe the world. According to this view, the disagreement in the metaphysics of composition about whether there are tables or only particles arranged table-wise is a trivial debate about linguistic preferences without any substantive consequences for the nature of reality.[123] The position that metaphysical disputes have no meaning or no significant point is calledmetaphysical orontological deflationism.[124] This view is opposed by so-calledserious metaphysicians, who contend that metaphysical disputes are about substantial features of the underlying structure of reality.[125] A closely related debate between ontologicalrealists and anti-realists concerns the question of whether there are any objective facts that determine which metaphysical theories are true.[126] A different criticism, formulated bypragmatists, sees the fault of metaphysics not in its cognitive ambitions or the meaninglessness of its statements, but in its practical irrelevance and lack of usefulness.[127]
Martin Heidegger criticized traditional metaphysics, saying that it fails to distinguish between individual entities and being as their ontological ground. His attempt to reveal the underlying assumptions and limitations in the history of metaphysics to "overcome metaphysics" influencedJacques Derrida's method ofdeconstruction.[128] Derrida employed this approach to criticize metaphysical texts for relying on opposing terms, like presence and absence, which he thought were inherently unstable and contradictory.[129]
There is no consensus about the validity of these criticisms and whether they affect metaphysics as a whole or only certain issues or approaches in it. For example, it could be the case that certain metaphysical disputes are merely verbal while others are substantive.[130]
Metaphysics is related to many fields of inquiry by investigating their basic concepts and relation to the fundamental structure of reality. For example, the natural sciences rely on concepts such aslaw of nature, causation, necessity, and spacetime to formulate their theories and predict or explain the outcomes of experiments.[131] While scientists primarily focus on applying these concepts to specific situations, metaphysics examines their general nature and how they depend on each other. For instance, physicists formulate laws of nature, likelaws of gravitation andthermodynamics, to describe how physical systems behave under various conditions. Metaphysicians, by contrast, examine what all laws of nature have in common, asking whether they merely describe contingent regularities or express necessary relations.[132] New scientific discoveries have also influenced existing metaphysical theories and inspired new ones. Einstein'stheory of relativity, for instance, prompted various metaphysicians to conceive space and time as a unified dimension rather than as independent dimensions.[133] Empirically focused metaphysicians often rely on scientific theories to ground their theories about the nature of reality in empirical observations.[134]
Similar issues arise in thesocial sciences where metaphysicians investigate their basic concepts and analyze their metaphysical implications. This includes questions like whether social facts emerge from non-social facts, whether social groups and institutions have mind-independent existence, and how they persist through time.[135] Metaphysical assumptions and topics inpsychology andpsychiatry include the questions about the relation between body and mind, whether the nature of the human mind is historically fixed, and what the metaphysical status of diseases is.[136]
Metaphysics is similar to bothphysical cosmology andtheology in its exploration of the first causes and the universe as a whole. Key differences are that metaphysics relies on rational inquiry while physical cosmology gives more weight to empirical observations and theology incorporates divinerevelation and other faith-based doctrines.[137] Historically, cosmology and theology were considered subfields of metaphysics.[138]
Computer scientists rely on metaphysics in the form of ontology to represent and classify objects. They develop conceptual frameworks, calledontologies, for limited domains,[140] such as a database with categories likeperson,company,address, andname to represent information about clients and employees.[141] Ontologies provide standards for encoding and storing information in a structured way, allowing computational processes to use the information for various purposes.[140]Upper ontologies, such asSuggested Upper Merged Ontology andBasic Formal Ontology, define concepts at a more abstract level, making it possible to integrate information belonging to different domains.[142]
Logic as the study ofcorrect reasoning[143] is often used by metaphysicians to engage in their inquiry and express insights through preciselogical formulas.[144] Another relation between the two fields concerns the metaphysical assumptions associated withlogical systems. Many logical systems likefirst-order logic rely onexistential quantifiers to express existential statements. For instance, in the logical formula the existential quantifier is applied to thepredicate to express that there are horses. Following Quine, various metaphysicians assume that existential quantifiers carryontological commitments, meaning that existential statements imply that the entities over which one quantifies are part of reality.[145]
Thetaijitu symbol showsyin and yang, which are two correlated forces discussed in Chinese metaphysics to explore the nature and patterns of existence.[146]
Metaphysics originated in the ancient period from speculations about the nature and origin of the cosmos.[147] Inancient India, starting in the 7th century BCE, theUpanishads were written as religious and philosophical texts that examine howultimate reality constitutes the ground of all being. They further explore the nature of theself and how it can reachliberation by understanding ultimate reality.[148] This period also saw the emergence ofBuddhism in the 6th century BCE,[o] which denies the existence of an independent self and understands the world as acyclic process.[150] At about the same time[p] inancient China, the school ofDaoism was formed and explored the natural order of the universe, known asDao, and how it is characterized by the interplay ofyin and yang as two correlated forces.[152]
Inancient Greece, metaphysics emerged in the 6th century BCE with thepre-Socratic philosophers, who gave rational explanations of the cosmos as a whole by examining thefirst principles from which everything arises.[153] Building on their work,Plato (427–347 BCE) formulated histheory of forms, which states that eternal forms or ideas possess the highest kind of reality while the material world is only an imperfect reflection of them.[154]Aristotle (384–322 BCE) accepted Plato's idea that there are universal forms but held that they cannot exist on their own but depend on matter. He also proposed a system of categories and developed a comprehensive framework of the natural world through his theory of thefour causes.[155] Starting in the 4th century BCE,Hellenistic philosophy explored therational order underlying the cosmos and the laws governing it.[156]Neoplatonism emerged towards the end of the ancient period in the 3rd century CE and introduced the idea of "the One" as the transcendent and ineffable source of all creation.[157][q]
Meanwhile, inIndian Buddhism, theMadhyamaka school developed the idea that all phenomena areinherently empty without a permanent essence. The consciousness-only doctrine of theYogācāra school stated that experienced objects are mere transformations of consciousness and do not reflect external reality.[159] TheHindu school ofSamkhya philosophy[r] introduced a metaphysical dualism withpure consciousness andmatter as its fundamental categories.[160] In China, the school ofXuanxue explored metaphysical problems such as the contrast between being and non-being.[161]
Boethius's theory of universals influenced many subsequent metaphysicians.
Medieval Western philosophy was profoundly shaped by ancient Greek thought as philosophers integrated these ideas withChristian philosophical teachings.Boethius (477–524 CE) sought to reconcile Plato's and Aristotle's theories of universals, proposing that universals can exist both in matter and mind. His theory inspired the development of nominalism and conceptualism, as in the thought ofPeter Abelard (1079–1142 CE).[162]Thomas Aquinas (1224–1274 CE) understood metaphysics as the discipline investigating different meanings ofbeing, such as the contrast between substance andaccident, and principles applying to all beings, such as theprinciple of identity.[163]William of Ockham (1285–1347 CE) developed a methodological principle, known asOckham's razor, to choose between competing metaphysical theories.[164] Arabic–Persian philosophy flourished fromthe early 9th century CE to the late 12th century CE, integrating ancient Greek philosophies to interpret and clarify the teachings of theQuran.[165]Avicenna (980–1037 CE) developed a comprehensive philosophical system that examined the contrast between existence and essence and distinguished between contingent and necessary existence.[166]Medieval India saw the emergence of themonist school ofAdvaita Vedanta in the 8th century CE, which holds that everything is one and that the idea of many entities existing independently is anillusion.[167] In China,Neo-Confucianism arose in the 9th century CE and explored theconcept of li as the rational principle that is the ground of being and reflects the order of the universe.[168]
In the early modern period and following renewed interest in Platonism during theRenaissance,René Descartes (1596–1650) developed a substance dualism according to which body and mind exist as independent entities that causally interact.[169] This idea was rejected byBaruch Spinoza (1632–1677), who formulated a monist philosophy suggesting that there is only one substance with both physical and mental attributes that develop side-by-side without interacting.[170]Gottfried Wilhelm Leibniz (1646–1716) introduced the concept of possible worlds and articulated a metaphysical system known asmonadology, which views the universe as a collection ofsimple substances synchronized without causal interaction.[171]Christian Wolff (1679–1754), conceptualized the scope of metaphysics by distinguishing between general and special metaphysics.[172] According to theidealism ofGeorge Berkeley (1685–1753), everything is mental, including material objects, which areideas perceived by the mind.[173]David Hume (1711–1776) made various contributions to metaphysics, including theregularity theory of causation and the idea that there are no necessary connections between distinct entities. Inspired by theempiricism ofFrancis Bacon (1561–1626) andJohn Locke (1632–1704), Hume criticized metaphysical theories that seek ultimate principles inaccessible to sensory experience.[174] This critical outlook was embraced byImmanuel Kant (1724–1804), who tried to reconceptualize metaphysics as an inquiry into the basic principles and categories of thought and understanding rather than seeing it as an attempt to comprehend mind-independent reality.[175]
At the turn of the 20th century inanalytic philosophy, philosophers such asBertrand Russell (1872–1970) andG. E. Moore (1873–1958) led a "revolt against idealism", arguing for the existence of a mind-independent world aligned with common sense and empirical science.[181]Logical atomists, like Russell and the earlyLudwig Wittgenstein (1889–1951), conceived the world as a multitude of atomic facts, which later inspired metaphysicians such asD. M. Armstrong (1926–2014).[182]Alfred North Whitehead (1861–1947) developedprocess metaphysics as an attempt to provide a holistic description of both the objective and the subjective realms.[183]
Rudolf Carnap (1891–1970) and otherlogical positivists formulated a wide-ranging criticism of metaphysical statements, arguing that they are meaningless because there is no way toverify them.[184] Other criticisms of traditional metaphysics identified misunderstandings ofordinary language as the source of many traditional metaphysical problems or challenged complex metaphysical deductions by appealing to common sense.[185]
The decline of logical positivism led to a revival of metaphysical theorizing.[186]Willard Van Orman Quine (1908–2000) tried to naturalize metaphysics by connecting it to the empirical sciences. His studentDavid Lewis (1941–2001) employed the concept of possible worlds to formulate hismodal realism.[187]Saul Kripke (1940–2022) helped revive discussions of identity andessentialism, distinguishingnecessity as a metaphysical notion from theepistemic notion ofa priori.[188]
Incontinental philosophy,Edmund Husserl (1859–1938) engaged in ontology through a phenomenological description of experience, while his studentMartin Heidegger (1889–1976) developedfundamental ontology to clarify the meaning of being.[189] Heidegger's philosophy inspiredJacques Derrida's (1930–2004) criticism of metaphysics.[190]Gilles Deleuze's (1925–1995) approach to metaphysics challenged traditionally influential concepts like substance, essence, and identity by reconceptualizing the field through alternative notions such as multiplicity, event, and difference.[191]
^Philosophers engaged in metaphysics are calledmetaphysicians ormetaphysicists.[2] Outside the academic discourse, the termmetaphysics is sometimes used in a different sense for the study ofoccult andparanormal phenomena, like metaphysical healing,auras, and thepower of pyramids.[3]
^For example, the metaphysical problem of causation is relevant both toepistemology, as a factor involved in perceptual knowledge, andethics, in regard to moral responsibility for the consequences caused by one'sactions.[8]
^The termontology is sometimes also used as a synonym of metaphysics as a whole.[16]
^Some philosophers use the termmetaontology as a synonym while others characterize metaontology as a subfield of meta-metaphysics.[24]
^According to Meinong, existence is not a synonym of being: all entities have being but not all entities have existence.[30]
^Although commonly labelledPlato's theory of forms, there is somescholarly disagreement about the extent to which this position belongs toSocrates rather than Plato.[33]
^Mereological problems were discussed as early as ancient Greek philosophy.[42]
^The positions of nominalism and conceptualism were formulated in medieval philosophy.[48]
^The classified entities do not have to occur naturally and can encompass man-made products, such as synthetic chemical substances.[49]
^A further topic concerns different types of modality, such as the contrast between physical, metaphysical, and logical necessity based on whether the necessity has its source in thelaws of nature, the essences of things, or the laws of logic.[54]
^For example, theconsequence argument byPeter van Inwagen says that people have no power over the future if everything is determined by the past together with the laws of nature.[86]
^The termintuition has a variety of other meanings in philosophy. It can refer to a simple opinion, a disposition to belief, what seems to be the case, or a relation between the mind and abstract objects.[103] The concept plays a central role in the philosophy ofImmanuel Kant, who understands intuitions as conscious, objective representations closely associated with the sense of space and time.[104]
^According to traditional accounts,Laozi as the founder of Daoism lived in the 6th century BCE but other accounts state that he may have lived in the 4th or 3rd centuries BCE.[151]
^The ideas underlying Samkhya philosophy arose as early as the 7th and 6th centuries BCE but its classical and systematic formulation is dated 350 CE.[160]
Audi, Robert (2006)."Philosophy". In Borchert, Donald M. (ed.).Encyclopedia of Philosophy. 7: Oakeshott – Presupposition (2. ed.). Thomson Gale, Macmillan Reference. pp. 325–337.ISBN978-0-02-865787-5.Archived from the original on 14 February 2022. Retrieved10 November 2023.
Baldwin, Tom (2010)."George Edward Moore".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved30 April 2024.
Berryman, Sylvia (2022)."Ancient Atomism".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 2 May 2019. Retrieved25 March 2024.
Berthrong, John H."Neo-Confucian Philosophy".Internet Encyclopedia of Philosophy.Archived from the original on 6 February 2024. Retrieved31 March 2024.
Berto, Francesco; Jago, Mark (2023)."Impossible Worlds".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 10 February 2021. Retrieved17 February 2024.
Bird, Alexander; Tobin, Emma (2024)."Natural Kinds".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved26 March 2024.
Blackburn, Simon (2008)."Existence".The Oxford Dictionary of Philosophy. Oxford University Press. p. 124.ISBN978-0-19-954143-0.Archived from the original on 10 August 2023. Retrieved1 September 2023.
Brown, Christopher M."Thomas Aquinas".Internet Encyclopedia of Philosophy.Archived from the original on 13 March 2024. Retrieved31 March 2024.
Brown, James Robert; Fehige, Yiftach (2019)."Thought Experiments".Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 21 November 2017. Retrieved29 October 2021.
Brzović, Zdenka."Natural Kinds".Internet Encyclopedia of Philosophy.Archived from the original on 13 March 2024. Retrieved26 March 2024.
Campbell, Keith (2006)."Ontology". In Borchert, Donald M. (ed.).Encyclopedia of Philosophy. 7: Oakeshott – Presupposition (2. ed.). Thomson Gale, Macmillan Reference. pp. 21–27.ISBN978-0-02-865787-5.Archived from the original on 29 January 2021. Retrieved21 March 2024.
Carroll, John W.; Markosian, Ned (2010).An Introduction to Metaphysics (1 ed.). Cambridge University Press.ISBN978-0-521-82629-7.
Casati, Filippo; Fujikawa, Naoya."Existence".Internet Encyclopedia of Philosophy.Archived from the original on 10 August 2023. Retrieved7 August 2023.
Chalmers, David J. (2009). "3. Ontological Anti-Realism".Metametaphysics: New Essays on the Foundations of Ontology. Clarendon Press. pp. 77–129.ISBN978-0-19-954604-6.
Cohen, S. Marc; Reeve, C. D. C. (2021)."Aristotle's Metaphysics".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 11 May 2020. Retrieved10 April 2024.
Craig, Edward (1998)."Metaphysics".Routledge Encyclopedia of Philosophy. Routledge.ISBN978-0-415-25069-6.Archived from the original on 1 August 2023. Retrieved19 March 2024.
Dafermos, Manolis (2021). "The Metaphysics of Psychology and a Dialectical Perspective".Theory & Psychology.31 (3):355–374.doi:10.1177/0959354320975491.
Dalal, Neil (2021)."Śaṅkara".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 27 January 2022. Retrieved2 April 2024.
Daly, Chris (2009)."To Be". In Poidevin, Robin Le; Peter, Simons; Andrew, McGonigal; Cameron, Ross P. (eds.).The Routledge Companion to Metaphysics. Routledge. pp. 225–233.ISBN978-1-134-15585-9.
Desmet, Ronald; Irvine, Andrew David (2022)."Alfred North Whitehead".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved1 April 2024.
Falguera, José L.; Martínez-Vidal, Concha; Rosen, Gideon (2022)."Abstract Objects".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 22 January 2021. Retrieved22 March 2024.
Gallois, Andre (2016)."Identity Over Time".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved28 March 2024.
Göhner, Julia F.; Schrenk, Markus."Metaphysics of Science".Internet Encyclopedia of Philosophy.Archived from the original on 7 April 2024. Retrieved7 April 2024.
Goldenbaum, Ursula."Geometrical Method".Internet Encyclopedia of Philosophy.Archived from the original on 7 March 2022. Retrieved15 March 2024.
Griffin, Nicholas (2013). "Russell and Moore's Revolt against British Idealism". In Beaney, Michael (ed.).The Oxford Handbook of The History of Analytic Philosophy. Oxford University Press. pp. 383–406.doi:10.1093/oxfordhb/9780199238842.013.0024.ISBN978-0-19-174978-0.
Hancock, Roger (2006). "Metaphysics, History of". In Borchert, Donald M. (ed.).The Encyclopedia of Philosophy. 6: Masaryk – Nussbaum (2 ed.). Thomson Gale, Macmillan Reference. pp. 183–197.ISBN978-0-02-865786-8.
Hawley, Katherine (2016)."Applied Metaphysics". In Lippert-Rasmussen, Kasper; Brownlee, Kimberley; Coady, David (eds.).A Companion to Applied Philosophy. John Wiley & Sons. pp. 165–179.ISBN978-1-118-86911-6.
Hawley, Katherine (2018). "Social Science as a Guide to Social Metaphysics?".Journal for General Philosophy of Science.49 (2):187–198.doi:10.1007/s10838-017-9389-5.hdl:10023/12888.
Hawley, Katherine (2023)."Temporal Parts".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved26 March 2024.
Hettche, Matt; Dyck, Corey (2019)."Christian Wolff".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 8 August 2019. Retrieved2 April 2024.
Heyndels, Sybren; Bengtson, Audun; Mesel, Benjamin De (2024)."Introduction".P. F. Strawson and His Philosophical Legacy. Oxford University Press. pp. 1–14.ISBN978-0-19-285847-4.
Hoad, T. F. (1993).The Concise Oxford Dictionary of English Etymology. Oxford University Press.ISBN978-0-19-283098-2.
Hofweber, Thomas (2023)."Logic and Ontology".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 7 December 2021. Retrieved20 March 2024.
Holland, Nancy J."Deconstruction".Internet Encyclopedia of Philosophy. Retrieved28 November 2024.
Houlgate, Stephen (2005).An Introduction to Hegel: Freedom, Truth and History (2 ed.). Blackwell.ISBN978-0-631-23063-2.
Janaway, Christopher (1999)."10. The Primacy of Will".Self and World in Schopenhauer's Philosophy. Oxford University Press. pp. 248–270.ISBN978-0-19-825003-6.Archived from the original on 2 April 2024. Retrieved4 April 2024.
Janiak, Andrew (2022)."Kant's Views on Space and Time".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved26 March 2024.
Kane, Robert (2011)."Introduction". In Kane, Robert (ed.).The Oxford Handbook of Free Will. Oxford University Press. pp. 1–35.ISBN978-0-19-987556-6.
Khlentzos, Drew (2021)."Challenges to Metaphysical Realism".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 26 September 2019. Retrieved18 March 2024.
Kirk, G. S. (2004)."Presocratics". In Rée, Jonathan; Urmson, J. O. (eds.).The Concise Encyclopedia of Western Philosophy. Routledge. pp. 308–317.ISBN978-1-134-33177-2.
Kirk, Robert (2023)."Zombies".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 28 September 2020. Retrieved15 March 2024.
Kirwan, Christopher (2005)."Identity".The Oxford Companion to Philosophy. Oxford University Press. pp. 417–418.ISBN978-0-19-926479-7.Archived from the original on 11 April 2024. Retrieved29 March 2024.
Klement, Kevin (2019)."Russell's Logical Atomism".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 11 April 2024. Retrieved2 April 2024.
Koons, Robert C.; Pickavance, Timothy H. (2015).Metaphysics: The Fundamentals (1. ed.). Wiley-Blackwell.ISBN978-1-4051-9574-4.
Korfmacher, Carsten."Personal Identity".Internet Encyclopedia of Philosophy.Archived from the original on 9 February 2021. Retrieved28 March 2024.
Kozierkiewicz, Adrianna; Pietranik, Marcin (2019)."A Formal Framework for the Ontology Evolution". In Nguyen, Ngoc Thanh; Gaol, Ford Lumban; Hong, Tzung-Pei; Trawiński, Bogdan (eds.).Intelligent Information and Database Systems: 11th Asian Conference, ACIIDS 2019, Yogyakarta, Indonesia, April 8–11, 2019, Proceedings, Part I. Springer. pp. 16–27.ISBN978-3-030-14799-0.
Lawson, Joanna (2020)."Common Sense in Metaphysics".The Cambridge Companion to Common-Sense Philosophy. Cambridge University Press. pp. 185–207.ISBN978-1-108-47600-3.Archived from the original on 18 March 2024. Retrieved18 March 2024.
Littlejohn, Ronnie."Daoist Philosophy".Internet Encyclopedia of Philosophy.Archived from the original on 29 March 2024. Retrieved30 March 2024.
Lizzini, Olga (2021)."Ibn Sina's Metaphysics".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 11 April 2024. Retrieved2 April 2024.
Look, Brandon C. (2020)."Gottfried Wilhelm Leibniz".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 5 August 2020. Retrieved2 April 2024.
Lorkowski, C. M."Hume, David: Causation".Internet Encyclopedia of Philosophy.Archived from the original on 27 March 2024. Retrieved27 March 2024.
Loux, Michael J.; Crisp, Thomas M. (2017).Metaphysics: A Contemporary Introduction (4 ed.). Routledge.ISBN978-1-138-63933-1.
Lowe, E. J. (2005a)."Truth".The Oxford Companion to Philosophy. Oxford University Press. pp. 926–927.ISBN978-0-19-926479-7.Archived from the original on 11 April 2024. Retrieved29 March 2024.
MacFarlane, John (2017)."Logical Constants".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 17 March 2020. Retrieved21 November 2021.
MacLeod, Mary C.; Rubenstein, Eric M."Universals".Internet Encyclopedia of Philosophy.Archived from the original on 24 February 2024. Retrieved24 March 2024.
Manley, David (2009). "1. Introduction: A Guided Tour of Metametaphysics".Metametaphysics: New Essays on the Foundations of Ontology. Clarendon Press. pp. 1–37.ISBN978-0-19-954604-6.
McLaughlin, Brian P. (1999). "Philosophy of Mind". In Audi, Robert (ed.).The Cambridge Dictionary of Philosophy (2 ed.). Cambridge University Press. pp. 684–694.ISBN978-0-521-63722-0.
McLean, G. F. (2003)."Metaphysics".New Catholic Encyclopedia. Gale and Catholic University of America.ISBN978-0-7876-4013-2.Archived from the original on 9 July 2021. Retrieved8 July 2021.
Menzel, Christopher (2023)."Possible Worlds".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved24 March 2024.
Morris, William Edward; Brown, Charlotte R. (2023)."David Hume".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 3 May 1998. Retrieved31 March 2024.
Morton, Adam (2005)."Mind".The Oxford Companion to Philosophy. Oxford University Press. p. 603.ISBN978-0-19-926479-7.
Mumford, Stephen; Tugby, Matthew (2013). "1. Introduction What Is the Metaphysics of Science?".Metaphysics and Science. Oxford University Press. pp. 3–28.ISBN978-0-19-967452-7.
Nelson, Michael (2022)."Existence".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 3 September 2018. Retrieved6 August 2023.
Noonan, Harold; Curtis, Ben (2022)."Identity".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 23 July 2020. Retrieved28 March 2024.
Oddie, Graham (2006). "Metaphysics". In Borchert, Donald M. (ed.).The Encyclopedia of Philosophy. 6: Masaryk – Nussbaum (2 ed.). Macmillan. pp. 169–183.ISBN978-0-02-865786-8.
Olson, Eric T. (2001)."Mind–Body Problem". In Blakemore, Colin; Jennett, Sheila (eds.).The Oxford Companion to the Body. Oxford University Press.ISBN978-0-19-852403-8.Archived from the original on 28 March 2024. Retrieved29 March 2024.
Olson, Eric T. (2023)."Personal Identity".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved28 March 2024.
O’Connor, Timothy; Franklin, Christopher (2022)."Free Will".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 15 May 2021. Retrieved28 March 2024.
Perkins, Franklin (2023)."Metaphysics in Chinese Philosophy".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 1 February 2024. Retrieved4 April 2024.
Proops, Ian (2022)."Wittgenstein's Logical Atomism".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved2 April 2024.
Pust, Joel (2019)."Intuition".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved8 August 2024.
Ramsey, William (2022)."Eliminative Materialism".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 14 October 2019. Retrieved27 March 2024.
Reynolds, Jack."Derrida, Jacques".Internet Encyclopedia of Philosophy.Archived from the original on 13 March 2024. Retrieved2 April 2024.
Roberts, John T. (2016)."16. Laws of Nature". In Humphreys, Paul (ed.).The Oxford Handbook of Philosophy of Science. Oxford University Press. pp. 337–355.ISBN978-0-19-063070-6.
Shapiro, Stewart; Kouri Kissel, Teresa (2022)."Classical Logic".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 3 May 1998. Retrieved15 August 2023.
Sider, Theodore (2009). "13. Ontological Realism".Metametaphysics: New Essays on the Foundations of Ontology. Clarendon Press. pp. 384–423.ISBN978-0-19-954604-6.
Smith, David Woodruff (2018)."Phenomenology".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved10 November 2024.
Smith, Daniel; Protevi, John; Voss, Daniela (2023)."Gilles Deleuze".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved11 August 2024.
Stern, Robert (2008). "Hegel's Idealism". In Beiser, Frederick C. (ed.).The Cambridge Companion to Hegel and Nineteenth-Century Philosophy. Cambridge University Press. pp. 135–173.ISBN978-1-139-82718-8.
Stern, Robert; Cheng, Tony (2023)."Transcendental Arguments".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved17 March 2024.
Stubenberg, Leopold; Wishon, Donovan (2023)."Neutral Monism".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 15 July 2018. Retrieved27 March 2024.
Studtmann, Paul (2024)."Aristotle's Categories".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved22 March 2024.
Thomasson, Amie (2022)."Categories".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 8 October 2023. Retrieved20 March 2024.
Timpe, Kevin."Free Will".Internet Encyclopedia of Philosophy.Archived from the original on 6 April 2019. Retrieved28 March 2024.
Turner, William (1911). "Metaphysics".Catholic Encyclopedia. Vol. 10. The Encyclopedia Press.OCLC1391341.
Van Inwagen, Peter (2023)."Existence".Encyclopedia Britannica.Archived from the original on 29 June 2023. Retrieved7 August 2023.
Van Inwagen, Peter; Sullivan, Meghan; Bernstein, Sara (2023)."Metaphysics".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 16 September 2018. Retrieved17 March 2024.
Varzi, Achille (2019)."Mereology".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 28 September 2020. Retrieved25 March 2024.
Velez, Abraham."Buddha".Internet Encyclopedia of Philosophy.Archived from the original on 4 February 2024. Retrieved30 March 2024.
Vihvelin, Kadri (2022)."Arguments for Incompatibilism".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved1 May 2024.
Wang, Yueqing; Bao, Qinggang; Guan, Guoxing (2020)."1. Way (Dao, 道)".History of Chinese Philosophy Through Its Key Terms. Nanjing University Press. pp. 1–18.ISBN978-981-15-2572-8.
Waxman, Wayne (2006)."David Hume (1711–1776)". In Borchert, Donald M. (ed.).The Encyclopedia of Philosophy. 4: Gadamer – Just War Theory (2 ed.). Macmillan. pp. 486–514.ISBN0-02-865784-5.
Weatherson, Brian (2023)."The Problem of the Many".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved19 November 2024.
Wheeler, Michael (2020)."Martin Heidegger".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved11 August 2024.
Wiland, Eric; Driver, Julia (2022)."Gertrude Elizabeth Margaret Anscombe".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved23 November 2024.
Wildberg, Christian (2021)."Neoplatonism".The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved22 November 2024.
Williamson, John (2012)."Probabilistic Theories". In Beebee, Helen; Hitchcock, Christopher; Menzies, Peter (eds.).The Oxford Handbook of Causation. Oxford University Press. pp. 185–212.ISBN978-0-19-162946-4.
Wood, Allen W. (2009)."Kantianism". In Kim, Jaekwon; Sosa, Ernest; Rosenkrantz, Gary S. (eds.).A Companion to Metaphysics. John Wiley & Sons. pp. 353–358.ISBN978-1-4443-0853-2.
