Introduction

This is the first chapter of this book whose title is a technical philosopher's word. That word—“metaphysics”—was first used as the name of a book by Aristotle, and what it means takes a certain amount of explanation.

The origin of the word “metaphysics” seems to have been this. The Greek adverb “meta” can mean “beyond.” Aristotle had written a book called the Physics, which was about what we would call “nat­ural science.” Aristotle (or his students) called the book that fol­lowed his Physics “the book beyond the Physics.” So, etymologically at least, metaphysics is the subject that comes after natural science.

But that, I fear, doesn't tell you very much. Certainly Aristotle did not think that he had invented the questions he was asking in the Metaphysics; he quotes and discusses the arguments of many previ­ous philosophers and poets. Still, much of this discussion, especially at the start of the book, is about the elements of which material things are made, and so it recapitulates some of the subject matter of the Physics. And, indeed, since physics in Aristotle's sense is the study of the natural world, it may seem to be rather difficult to see what else there is to study “after” or “beyond” physics. What, after all, is there except the natural world?

Aristotle himself, in the second book of the Metaphysics (which may originally have been intended to be a preface to the Physics), discusses some concepts that we need before we can begin to think about the natural world at all, among them the notion of a cause. In other places he discusses such concepts as element, nature, neces­sity, unity, being, identity, potentiality, and truth, as well as many other concepts.

Well, in 4.13, in our discussion of causality, we noticed that in the sciences we try to discover laws, generalizations that are true nei­ther, at one extreme, just in the actual possible world nor, at another extreme, in all the possible worlds, but rather in the class of nomi- cally possible worlds. The laws of physics aren't necessary in the sense of true in every possible world: the gravitational constant, g, could presumably have had a different value from the one that it does, and then falling bodies would have accelerated faster or slower toward the Earth. So, clearly, one possible subject matter that goes beyond natural science is what general truths obtain not just in the nomically possible worlds—the worlds with the same nat­ural laws as the actual world—but in larger classes of worlds and, perhaps, in the end, in all of the possible worlds. (I'm going to need to be able to talk about possible worlds where the laws of nature don't hold, so I'll call them the “nomically impossible worlds.”)

8.2