Metaphysics

Metaphysics is the branch of philosophy that examines the basic structure of reality. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the fundamental categories of human understanding. Some philosophers, including Aristotle, designate metaphysics as first 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 of existence, the features all entities have in common, and their division into categories of being. An influential division is between particulars and universals. Particulars are individual unique entities, like a specific apple. Universals are general features that different particulars have in common, like the color red. Modal metaphysics examines what it means for something to be possible or necessary. Metaphysicians also explore the concepts of space, time, and change, and their connection to causality and the laws of nature. Other topics include how mind and matter are related, whether everything in the world is predetermined, and whether there is free will.

Metaphysicians use various methods to conduct their inquiry. Traditionally, they rely on rational intuitions and abstract reasoning but have recently included empirical 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 roots of metaphysics lie in antiquity with speculations about the nature and origin of the universe, like those found in the Upanishads in ancient India, Daoism in ancient China, and pre-Socratic philosophy in ancient Greece. During the subsequent medieval period in the West, discussions about the nature of universals were influenced by the philosophies of Plato and Aristotle. The modern period saw the emergence of various comprehensive systems of metaphysics, many of which embraced idealism. In the 20th century, traditional metaphysics in general and idealism in particular faced various criticisms, which prompted new approaches to metaphysical inquiry.

Metaphysics is the study of the most general features of reality, including existence, objects and their properties, possibility and necessity, space and time, change, causation, and the relation between matter and mind. It is one of the oldest branches of philosophy.^[1][a]

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 the essences 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 in ancient and medieval philosophy understand metaphysics as the science of the first causes and as the study of being qua 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 and free will.^[6] Some philosophers follow Aristotle 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]

Metaphysics is traditionally understood as a study of mind-independent features of reality. Starting with Immanuel Kant's critical 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 critical metaphysics, which outlines the aspects and principles underlying all human thought and experience.^[9] Philosopher P. 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 in physics, living entities in biology, and cultures in anthropology.^[11] It is disputed to what extent this contrast is a strict dichotomy rather than a gradual continuum.^[12]

Metaphysicians employ a variety of methods to develop metaphysical theories and formulate arguments for and against them.^[94] Traditionally, a priori methods have been the dominant approach. They rely on rational intuition and abstract reasoning from general principles rather than sensory experience. A posteriori approaches, by contrast, ground metaphysical theories in empirical observations and scientific theories.^[95] Some metaphysicians incorporate perspectives from fields such as physics, psychology, linguistics, and history into their inquiry.^[96] The two approaches are not mutually exclusive: it is possible to combine elements from both.^[97] 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, as metaphysical realists claim, or the principles underlying thought and experience, as some metaphysical anti-realists contend.^[98]

A priori approaches often rely on intuitions—non-inferential impressions about the correctness of specific claims or general principles.^[99][k] For example, arguments for the A-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.^[102] Some approaches use intuitions to establish a small set of self-evident fundamental principles, known as axioms, and employ deductive reasoning to build complex metaphysical systems by drawing conclusions from these axioms.^[103] Intuition-based approaches can be combined with thought experiments, which help evoke and clarify intuitions by linking them to imagined situations. They use counterfactual thinking to assess the possible consequences of these situations.^[104] For example, to explore the relation between matter and consciousness, some theorists compare humans to philosophical zombies—hypothetical creatures identical to humans but without conscious experience.^[105] A related method relies on commonly accepted beliefs instead of intuitions to formulate arguments and theories. The common-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 that mereological nihilism is false since it implies that commonly accepted things, like tables, do not exist.^[106]

Conceptual analysis, a method particularly prominent in analytic philosophy, aims to decompose metaphysical concepts into component parts to clarify their meaning and identify essential relations.^[107] In phenomenology, the method of eidetic variation is used to investigate essential structures underlying phenomena. This method involves imagining an object and varying its features to determine which ones are essential and cannot be changed.^[108] The transcendental method is a further approach and examines the metaphysical structure of reality by observing what entities there are and studying the conditions of possibility without which these entities could not exist.^[109]

Some approaches give less importance to a 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 as naturalized metaphysics and is closely associated with the work of Willard Van Orman Quine.^[110] He relies on the idea that true sentences from the sciences and other fields have ontological commitments, that is, they imply that certain entities exist.^[111] 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.^[112] Quine used this insight to argue that one can learn about metaphysics by closely analyzing^[l] scientific claims to understand what kind of metaphysical picture of the world they presuppose.^[114]

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 consider explanatory power, theoretical usefulness, and proximity to established beliefs.^[115]

Despite its status as one of the main branches of philosophy, metaphysics has received numerous criticisms questioning its legitimacy as a field of inquiry.^[116] One criticism argues that metaphysical inquiry is impossible because humans lack the cognitive capacities needed to access the ultimate nature of reality.^[117] This line of thought leads to skepticism about the possibility of metaphysical knowledge. Empiricists often follow this idea, like Hume, who argued that there is no good source of metaphysical knowledge since metaphysics lies outside the field of empirical knowledge and relies on dubious intuitions about the realm beyond sensory experience. A related argument favoring the unreliability of metaphysical theorizing points to the deep and lasting disagreements about metaphysical issues, suggesting a lack of overall progress.^[118]

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 but meaningless. According to logical positivists, for instance, the meaning of a statement is given by the procedure used to verify it, usually through the observations that would confirm it. Based on this controversial assumption, they argue that metaphysical statements are meaningless since they make no testable predictions about experience.^[119]

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.^[120] The position that metaphysical disputes have no meaning or no significant point is called metaphysical or ontological deflationism.^[121] This view is opposed by so-called serious metaphysicians, who contend that metaphysical disputes are about substantial features of the underlying structure of reality.^[122] A closely related debate between ontological realists and anti-realists concerns the question of whether there are any objective facts that determine which metaphysical theories are true.^[123] A different criticism, formulated by pragmatists, 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.^[124]

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" influenced Jacques Derrida's method of deconstruction.^[125] 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.^[126]

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.^[127]

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 as law of nature, causation, necessity, and spacetime to formulate their theories and predict or explain the outcomes of experiments.^[128] 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, like laws of gravitation and thermodynamics, 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.^[129] New scientific discoveries have also influenced existing metaphysical theories and inspired new ones. Einstein's theory of relativity, for instance, prompted various metaphysicians to conceive space and time as a unified dimension rather than as independent dimensions.^[130] Empirically focused metaphysicians often rely on scientific theories to ground their theories about the nature of reality in empirical observations.^[131]

Similar issues arise in the social 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.^[132] Metaphysical assumptions and topics in psychology and psychiatry 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.^[133]

Metaphysics is similar to both physical cosmology and theology 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 divine revelation and other faith-based doctrines.^[134] Historically, cosmology and theology were considered subfields of metaphysics.^[135]

Metaphysics in the form of ontology plays a central role in computer science to classify objects and formally represent information about them. Unlike metaphysicians, computer scientists are usually not interested in providing a single all-encompassing characterization of reality as a whole. Instead, they employ many different ontologies, each one concerned only with a limited domain of entities.^[137] For instance, an organization may use an ontology with categories such as person, company, address, and name to represent information about clients and employees.^[138] Ontologies provide standards or conceptualizations for encoding and storing information in a structured way, enabling computational processes to use and transform their information for a variety of purposes.^[137] Some knowledge bases integrate information from various domains, which brings with it the challenge of handling data that was formulated using diverse ontologies. They address this by providing an upper ontology that defines concepts at a higher level of abstraction, applicable to all domains. Influential upper ontologies include Suggested Upper Merged Ontology and Basic Formal Ontology.^[139]

Logic as the study of correct reasoning^[140] is often used by metaphysicians to engage in their inquiry and express insights through precise logical formulas.^[141] Another relation between the two fields concerns the metaphysical assumptions associated with logical systems. Many logical systems like first-order logic rely on existential quantifiers to express existential statements. For instance, in the logical formula ${\displaystyle \exists x{\text{Horse}}(x)}$ the existential quantifier ${\displaystyle \exists }$ is applied to the predicate ${\displaystyle {\text{Horse}}}$ to express that there are horses. Following Quine, various metaphysicians assume that existential quantifiers carry ontological commitments, meaning that existential statements imply that the entities over which one quantifies are part of reality.^[142]

Metaphysics originated in the ancient period from speculations about the nature and origin of the cosmos.^[144] In ancient India, starting in the 7th century BCE, the Upanishads were written as religious and philosophical texts that examine how ultimate reality constitutes the ground of all being. They further explore the nature of the self and how it can reach liberation by understanding ultimate reality.^[145] This period also saw the emergence of Buddhism in the 6th century BCE,^[m] which denies the existence of an independent self and understands the world as a cyclic process.^[147] At about the same time^[n] in ancient China, the school of Daoism was formed and explored the natural order of the universe, known as Dao, and how it is characterized by the interplay of yin and yang as two correlated forces.^[149]

In ancient Greece, metaphysics emerged in the 6th century BCE with the pre-Socratic philosophers, who gave rational explanations of the cosmos as a whole by examining the first principles from which everything arises.^[150] Building on their work, Plato (427–347 BCE) formulated his theory 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.^[151] 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 the four causes.^[152] Starting in the 4th century BCE, Hellenistic philosophy explored the rational order underlying the cosmos and the idea that it is made up of indivisible atoms.^[153] 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.^[154][o]

Meanwhile, in Indian Buddhism, the Madhyamaka school developed the idea that all phenomena are inherently empty without a permanent essence. The consciousness-only doctrine of the Yogācāra school stated that experienced objects are mere transformations of consciousness and do not reflect external reality.^[156] The Hindu school of Samkhya philosophy^[p] introduced a metaphysical dualism with pure consciousness and matter as its fundamental categories.^[157] In China, the school of Xuanxue explored metaphysical problems such as the contrast between being and non-being.^[158]

Medieval Western philosophy was profoundly shaped by ancient Greek philosophy. 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 of Peter Abelard (1079–1142 CE).^[159] Thomas Aquinas (1224–1274 CE) understood metaphysics as the discipline investigating different meanings of being, such as the contrast between substance and accident, and principles applying to all beings, such as the principle of identity.^[160] William of Ockham (1285–1347 CE) proposed Ockham's razor, a methodological principles to choose between competing metaphysical theories.^[161] Arabic–Persian philosophy flourished from the early 9th century CE to the late 12th century CE, integrating ancient Greek philosophies to interpret and clarify the teachings of the Quran.^[162] Avicenna (980–1037 CE) developed a comprehensive philosophical system that examined the contrast between existence and essence and distinguished between contingent and necessary existence.^[163] Medieval India saw the emergence of the monist school of Advaita Vedanta in the 8th century CE, which holds that everything is one and that the idea of many entities existing independently is an illusion.^[164] In China, Neo-Confucianism arose in the 9th century CE and explored the concept of li as the rational principle that is the ground of being and reflects the order of the universe.^[165]

In the early modern period, René Descartes (1596–1650) developed a substance dualism according to which body and mind exist as independent entities that causally interact.^[166] This idea was rejected by Baruch 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.^[167] Gottfried Wilhelm Leibniz (1646–1716) introduced the concept of possible worlds and articulated a metaphysical system known as monadology, which views the universe as a collection of simple substances synchronized without causal interaction.^[168] Christian Wolff (1679–1754), conceptualized the scope of metaphysics by distinguishing between general and special metaphysics.^[169] According to the idealism of George Berkeley (1685–1753), everything is mental, including material objects, which are ideas perceived by the mind.^[170] David Hume (1711–1776) made various contributions to metaphysics, including the regularity theory of causation and the idea that there are no necessary connections between distinct entities. Inspired by the empiricism of Francis Bacon (1561–1626) and John Locke (1632–1704), Hume criticized metaphysical theories that seek ultimate principles inaccessible to sensory experience.^[171] This critical outlook was embraced by Immanuel 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.^[172]

Many developments in the later modern period were shaped by Kant's philosophy. German idealists adopted his idealistic outlook in their attempt to find a unifying principle as the foundation of all reality.^[173] Georg Wilhelm Friedrich Hegel (1770–1831) developed a comprehensive system of philosophy that examines how absolute spirit manifests itself.^[174] He inspired the British idealism of Francis Herbert Bradley (1846–1924), who interpreted absolute spirit as the all-inclusive totality of being.^[175] Arthur Schopenhauer (1788–1860) was a strong critic of German idealism and articulated a different metaphysical vision, positing a blind and irrational will as the underlying principle of reality.^[176] Pragmatists like C. S. Peirce (1839–1914) and John Dewey (1859–1952) conceived metaphysics as an observational science of the most general features of reality and experience.^[177]

At the turn of the 20th century in analytic philosophy, philosophers such as Bertrand Russell (1872–1970) and G. 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.^[178] Logical atomists, like Russell and the early Ludwig Wittgenstein (1889–1951), conceived the world as a multitude of atomic facts, which later inspired metaphysicians such as D. M. Armstrong (1926–2014).^[179] Alfred North Whitehead (1861–1947) developed process metaphysics as an attempt to provide a holistic description of both the objective and the subjective realms.^[180]

Rudolf Carnap (1891–1970) and other logical positivists formulated a wide-ranging criticism of metaphysical statements, arguing that they are meaningless because there is no way to verify them.^[181] Other criticisms of traditional metaphysics identified misunderstandings of ordinary language as the source of many traditional metaphysical problems or challenged complex metaphysical deductions by appealing to common sense.^[182]

The decline of logical positivism led to a revival of metaphysical theorizing.^[183] Willard Van Orman Quine (1908–2000) tried to naturalize metaphysics by connecting it to the empirical sciences. His student David Lewis (1941–2001) employed the concept of possible worlds to formulate his modal realism.^[184] Saul Kripke (1940–2022) helped revive discussions of identity and essentialism, distinguishing necessity as a metaphysical notion from the epistemic notion of a priori.^[185]

In continental philosophy, Edmund Husserl (1859–1938) engaged in ontology through a phenomenological description of experience, while his student Martin Heidegger (1889–1976) developed fundamental ontology to clarify the meaning of being.^[186] Heidegger's philosophy inspired general criticisms of metaphysics by postmodern thinkers like Jacques Derrida (1930–2004).^[187] 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.^[188]

• Computational metaphysics
• Doctor of Metaphysics
• Enrico Berti's classification of metaphysics
• Feminist metaphysics
• Fundamental question of metaphysics
• List of metaphysicians
• Metaphysical grounding