Metaphysics is a branch of philosophy that investigates principles of reality transcending those of any particular science. Cosmology and ontology are traditional branches of metaphysics. It is concerned with explaining the fundamental nature of being and the world. Someone who studies metaphysics would be called either a "metaphysician" or a "metaphysicist."
The word derives from the Greek words meta (meaning "beyond" or "after") and physika (meaning "physical"), "physical" referring to those works on matter by Aristotle in antiquity. The prefix meta- ("beyond") was attached to the chapters in Aristotle's work that physically followed after the chapters on "physics," in posthumously edited collections. Aristotle himself did not call these works Metaphysics. Aristotle called some of the subjects treated there "first philosophy."
A central branch of metaphysics is ontology, the investigation into what types of things there are in the world and what relations these things bear to one another. The metaphysician also attempts to clarify the notions by which people understand the world, including existence, objecthood, property, space, time, causality, and possibility.
Before the development of modern science, scientific questions were addressed as a part of metaphysics known as "natural philosophy"; the term "science" itself meant "knowledge" of epistemological origin. The scientific method, however, made natural philosophy an empirical and experimental activity unlike the rest of philosophy, and by the end of the eighteenth century it had begun to be called "science" in order to distinguish it from philosophy. Thereafter, metaphysics became the philosophical enquiry of a non-empirical character into the nature of existence.
Metaphysics is generally taken to mean philosophical speculation beyond the current or even seemingly possible limits of science or technology to test, the development of systems intended to explain origins and purpose, and the place of man in the universe. The word 'metaphysics' has its origin simply from those books of Aristotle which were placed in sequence after his Physics. The pejorative sense of 'obscure' and 'over-speculative' is recent, especially following attempts by A. J. Ayer and others to show that metaphysics is strictly nonsense.
In the history of Western philosophy, metaphysics has been understood in various ways: as an inquiry into what basic categories of things there are (e.g., the mental and the physical); as the study of reality, as opposed to appearance; as the study of the world as a whole; and as a theory of first principles. Some basic problems in the history of metaphysics are the problem of universals — i.e., the problem of the nature of universals and their relation to so-called particulars; the existence of God; the mind-body problem; and the problem of the nature of material, or external, objects. Major types of metaphysical theory include Platonism, Aristotelianism, Thomism, Cartesianism (see also dualism), idealism, realism, and materialism.
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