Metaphysics is the branch of philosophy that studies the first principles of being, identity and change, space and time, causality, necessity and possibility. It includes questions about the nature of consciousness and the relationship between mind and matter. The word "metaphysics" comes from two Greek words that, together, literally mean "after or behind or among [the study of] the natural". It has been suggested that the term might have been coined by a first century CE editor who assembled various small selections of Aristotle’s works into the treatise we now know by the name Metaphysics (μετὰ τὰ φυσικά, meta ta physika, lit. 'after the Physics ', another of Aristotle's works).
Metaphysics studies questions related to what it is for something to exist and what types of existence there are. Metaphysics seeks to answer, in an abstract and fully general manner, the questions:
- What is there?
- What is it like?
Topics of metaphysical investigation include existence, objects and their properties, space and time, cause and effect, and possibility. Metaphysics is considered one of the four main branches of philosophy, along with epistemology, logic, and ethics.
There are two broad stances about what is "the world" studied by metaphysics. According to metaphysical realism, the objects studied by metaphysics exist independently of any observer so that the subject is the most fundamental of all sciences. Metaphysical anti-realism, on the other hand, assumes that the objects studied by metaphysics exist inside the mind of an observer, so the subject becomes a form of introspection and conceptual analysis. This position is of more recent origin.
Some philosophers, notably Kant, discuss both of these "worlds" and what can be inferred about each one. Some, such as the logical positivists, and many scientists, reject the metaphysical realism as meaningless and unverifiable. Others reply that this criticism also applies to any type of knowledge, including hard science, which claims to describe anything other than the contents of human perception, and thus that the world of perception is the objective world in some sense. Metaphysics itself usually assumes that some stance has been taken on these questions and that it may proceed independently of the choice—the question of which stance to take belongs instead to another branch of philosophy, epistemology.
Metaphysical cosmology is the branch of metaphysics that deals with the world as the totality of all phenomena in space and time. Historically, it formed a major part of the subject alongside Ontology, though its role is more peripheral in contemporary philosophy. It has had a broad scope, and in many cases was founded in religion. The ancient Greeks drew no distinction between this use and their model for the cosmos. However, in modern times it addresses questions about the Universe which are beyond the scope of the physical sciences. It is distinguished from religious cosmology in that it approaches these questions using philosophical methods (e.g. dialectics).
Cosmogony deals specifically with the origin of the universe. Modern metaphysical cosmology and cosmogony try to address questions such as:
- What is the origin of the Universe? What is its first cause? Is its existence necessary?
- What are the ultimate material components of the Universe?
- What is the ultimate reason for the existence of the Universe? Does the cosmos have a purpose?
Although metaphysics as a philosophical enterprise is highly hypothetical, it also has practical application in most other branches of philosophy, science, and now also information technology. Such areas generally assume some basic ontology (such as a system of objects, properties, classes, and space-time) as well as other metaphysical stances on topics such as causality and agency, then build their own particular theories upon these.
"Social" branches of philosophy such as philosophy of morality, aesthetics and philosophy of religion (which in turn give rise to practical subjects such as ethics, politics, law, and art) all require metaphysical foundations, which may be considered as branches or applications of metaphysics. For example, they may postulate the existence of basic entities such as value, beauty, and God. Then they use these postulates to make their own arguments about consequences resulting from them. When philosophers in these subjects make their foundations they are doing applied metaphysics, and may draw upon its core topics and methods to guide them, including ontology and other core and peripheral topics. As in science, the foundations chosen will in turn depend on the underlying ontology used, so philosophers in these subjects may have to dig right down to the ontological layer of metaphysics to find what is possible for their theories. For example, a contradiction obtained in a theory of God or Beauty might be due to an assumption that it is an object rather than some other kind of ontological entity.