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 unique individual 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. They typically rely on rational intuitions and abstract reasoning but also include 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, Taoism 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.
Definition
Metaphysics is the study of the most elementary 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.
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. Some definitions are descriptive by providing an account of what metaphysicians do while others are normative and prescribe what metaphysicians ought to do.
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 has expanded to include topics such as the distinction between mind and body and free will.
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.
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 the critical perspective on metaphysics, which outlines the aspects and principles underlying all human thought and experience.
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.
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. It is disputed to what extent this contrast is a strict dichotomy rather than a gradual continuum.
Etymology
The word metaphysics has its origin in the ancient Greek words metรก (ฮผฮตฯฮฌ, meaning 'after', 'above', and 'beyond') and phusikรก (ฯฯ ฯฮนฮบฮฌ), as a short form of ta metรก ta phusikรก, 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.
Alternatively, metaphysics may have received its name by a historical accident when Aristotle's book on this subject, Metaphysics, was published. Aristotle himself did not use the term metaphysics but an editor of his works some two centuries later (likely Andronicus of Rhodes) coined it for the title, presumably to indicate that this book should be studied after Aristotle's book Physics: thus, literally 'after physics'. The term entered the English language in the mid 1500s through the Latin word metaphysica.
Branches
The nature of metaphysics can also be characterized in relation to its main branches. An influential division from early modern philosophy distinguishes between general and special or specific metaphysics. General metaphysics, also called ontology, 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 different categories. Categories are the most general kinds, such as substance, property, relation, and fact. 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.
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 a world as a totality extending through space and time. 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. The scope of special metaphysics overlaps with other philosophical disciplines, making it unclear whether a topic belongs to it or to areas like philosophy of mind and theology.
Starting in the second half of the 20th century, applied metaphysics was conceived as the area of applied philosophy examining the implications and uses of metaphysics, both within philosophy and other fields of inquiry. In areas like ethics and philosophy of religion, it addresses topics like the ontological foundations of moral claims and religious doctrines.
Beyond philosophy, its applications include the use of ontologies in artificial intelligence, economics, and sociology to classify entities. In psychiatry and medicine, it examines the metaphysical status of diseases.
Meta-metaphysics is the metatheory 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.
Topics
Existence and categories of being
Metaphysicians often regard existence or being as one of the most basic and general concepts. To exist means to be part of reality, distinguishing real entities from imaginary ones. According to a traditionally influential view, existence is a property of properties: if an entity exists then its properties are instantiated.
A different position states that existence is a property of individuals, meaning that it is similar to other properties, such as shape or size. It is controversial whether all entities have this property. According to philosopher Alexius Meinong, there are nonexistent objects, including merely possible objects like Santa Claus and Pegasus.
A related question is whether existence is the same for all entities or whether there are different modes or degrees of existence. For instance, Plato held that Platonic forms, which are perfect and immutable ideas, have a higher degree of existence than matter, which can only imperfectly reflect Platonic forms.
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. One of the earliest theories of categories was proposed by Aristotle, who outlined a system of 10 categories.
He argued that substances (e.g., man and horse), are the most important category since all other categories like quantity (e.g., four), quality (e.g., white), and place (e.g., in Athens) are said of substances and depend on them. Kant understood categories as fundamental principles underlying human understanding and developed a system of 12 categories, divided into the four classes: quantity, quality, relation, and modality.
More recent theories of categories were proposed by C. S. Peirce, Edmund Husserl, Samuel Alexander, Roderick Chisholm, and E. J. Lowe. Many philosophers rely on the contrast between concrete 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, like numbers and sets, which do not exist in space and time, are immutable, and do not engage in causal relations.
Particulars
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 with universals, like the color red, which can at the same time exist in several places and characterize several particulars.
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 with John Locke's philosophy, analyzes each particular as a substratum, also called bare 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 by bundle theorists. Inspired by David 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, called haecceity following scholastic terminology, to ensure that each bundle is unique. Another proposal for concrete particulars is that they are individuated by their space-time location.
Concrete particulars encountered in everyday life, like rocks, tables, and organisms, are complex entities composed 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 by mereology. 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.
A related mereological problem is whether there are simple entities that have no proper parts, as atomists claim, or whether everything can be endlessly subdivided into smaller parts, as continuum theorists contend.
Universals
Universals are general entities, encompassing both properties and relations, 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 particulars Nelson Mandela and Mahatma Gandhi instantiate the universal humanity, similar to how a strawberry and a ruby instantiate the universal red.
A topic discussed since ancient philosophy, the problem of universals consists in the challenge of characterizing the ontological status of universals. Realists argue that universals are real, mind-independent entities that exist in addition to particulars. According to Platonic realists, universals exist independently of particulars, which implies that the universal red would continue to exist even if there were no red things.
A more moderate 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 as concepts in the mind used to order experience by classifying entities.
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, usually by the natural sciences, and include kinds like electrons, H2O, and tigers.
Scientific realists and anti-realists disagree about whether natural kinds exist. Social kinds, like money and baseball, are studied by social metaphysics and characterized as useful social constructions that, while not purely fictional, do not reflect the fundamental structure of mind-independent reality.
Possibility and necessity
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.
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. 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 to fictional statements.
Borrowing a term from German philosopher Gottfried Wilhelm Leibniz's theodicy, many metaphysicians use the concept of possible 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. For example, the dinosaurs were wiped out in the actual world but there are possible worlds in which they are still alive.
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. 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 by counterparts.
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 of fiction.
Space, time, and change
Space and time 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. 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 of being next to and the temporal relation of coming before.
In the metaphysics of time, an important contrast is between the A-series and the B-series. According to the A-series theory, the flow 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. Eternalism holds that past, present, and future are equally real, whereas presentism asserts that only entities in the present exist.
Material objects persist through time and change in the process, like a tree that grows or loses leaves. The main ways of conceptualizing persistence through time are endurantism and perdurantism. 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 different temporal 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.
Causality
Causality is the relation between cause and effect whereby one entity produces or alters another entity. For instance, if a person bumps a glass and spills its contents then the bump is the cause and the spill is the effect. Besides the single-case causation between particulars in this example, there is also general-case causation expressed in statements such as "smoking causes cancer".
The term agent causation is used when people and their actions cause something. Causation is usually interpreted deterministically, meaning that a cause always brings about its effect. However, some philosophers such as G. E. M. Anscombe have provided counterexamples to this idea. Such counterexamples have inspired the development of probabilistic 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.
The regularity theory of causation, inspired by David Hume's philosophy, states that causation is nothing but a constant 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. According to nomic regularity theories, regularities manifest as laws of nature studied by science.
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. 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. Eliminativists reject the above theories by holding that there is no causation.
Mind and free will
Mind encompasses phenomena like thinking, perceiving, feeling, and desiring as well as the underlying faculties responsible for these phenomena. The mindโbody problem is the challenge of clarifying the relation between physical and mental phenomena. According to Cartesian 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. This view is rejected by monists, who argue that reality is made up of only one kind. According to metaphysical idealism, everything is mental or dependent on the mind, including physical objects, which may be understood as ideas or perceptions of conscious minds.
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, behavioral dispositions, or functional roles. Neutral monists argue that reality is fundamentally neither material nor mental and suggest that matter and mind are both derivative phenomena.
A key aspect of the mindโbody problem is the hard problem of consciousness or how to explain that physical systems like brains can produce phenomenal consciousness.