XV—The Physical World

Abstract

What sort of thing is the physical world? I do not ask for details about what the world is like that might be supplied by the physical sciences. I have in mind the appeal to the physical world that is made in philosophy, especially in the metaphysical thesis of materialism or physicalism: the world is purely physical, or the physical world is the only world there is, or the only world that is real. Traditionally, materialism was a thesis about objects-only bodies exist, the only things that exist are material things, the world contains nothing but physical entities. It was a monism of physical substances, as opposed to a dualism of bodies and minds, or an idealism of only minds. But what the world is like is not settled just by what sorts of things are in it. Given the very same collection of things, you could have quite different worlds, depending on how those things were related to each other and how they behaved. What is true of the things that exist counts just as much for what the world is like as what sorts of things there are. Why philosophers have traditionally gone in for classifying or counting the number of kinds of objects there are, as opposed to asking what is true, is a big and difficult question which still needs an answer. Perhaps part of the explanation is the thought that the sorts of things that exist put limits on what the world could be like by restricting what is true of the things that exist. If the 'essence' of body was extension, for example, and only bodies existed, then everything that was true of what exists had to be a 'mode' of extension, since bodies could have only those properties that are 'modes' of their essential property. What the world is like in general could be deduced from the essences of the things it contains. Whatever its source, ontology has been the attempt to answer the question 'What is there?' or 'What exists?' But that alone would not tell us what the world is like. That can be done only by saying what is true of the things that exist, not