It is not easy to say what metaphysics is. Ancient and Medieval philosophers might have said that metaphysics was, like chemistry or astrology, to be defined by its subject matter: metaphysics was the “science” that studied “being as such” or “the first causes of things” or “things that do not change”. It is no longer possible to define metaphysics that way, for two reasons. First, a philosopher who denied the existence of those things that had once been seen as constituting the subject-matter of metaphysics—first causes or unchanging things—would now be considered to be making thereby a metaphysical assertion. Second, there are many philosophical problems that are now considered to be metaphysical problems (or at least partly metaphysical problems) that are in no way related to first causes or unchanging things—the problem of free will, for example, or the problem of the mental and the physical.
Metaphysics is the branch of philosophy which considers the ultimate nature of reality.
Of course, since philosophy concerns itself with questions that can’t be answered by scientific investigation, many questions about the nature of reality, like “Are their black holes?” and “What is the chemical composition of water?”, aren’t really metaphysical. Other questions about reality, however – questions like “Doe God exist?” and “Do we have free will?” – are probably destined to elude empirical resolution and so are genuinely philosophical. It’s this sort of question that metaphysics addresses.
Immanuel Kant (1724-1804) is one of the most influential philosophers in the history of Western philosophy. His contributions to metaphysics, epistemology, ethics, and aesthetics have had a profound impact on almost every philosophical movement that followed him. This article focuses on his metaphysics and epistemology in one of his most important works, The Critique of Pure Reason. A large part of Kant’s work addresses the question “What can we know?” The answer, if it can be stated simply, is that our knowledge is constrained to mathematics and the science of the natural, empirical world. It is impossible, Kant argues, to extend knowledge to the supersensible realm of speculative metaphysics. The reason that knowledge has these constraints, Kant argues, is that the mind plays an active role in constituting the features of experience and limiting the mind’s access only to the empirical realm of space and time.
The first major work in the history of philosophy to bear the title “Metaphysics” was the treatise by Aristotle that we have come to know by that name. But Aristotle himself did not use that title or even describe his field of study as ‘metaphysics’; the name was evidently coined by the first century C.E. editor who assembled the treatise we know as Aristotle’s Metaphysics out of various smaller selections of Aristotle’s works. The title ‘metaphysics’—literally, ‘after the Physics’—very likely indicated the place the topics discussed therein were intended to occupy in the philosophical curriculum. They were to be studied after the treatises dealing with nature (ta phusika). In this entry, we discuss the ideas that are developed in Aristotle’s treatise.