Possible words

In Chapter 2 I outlined a theory of our world, and what the fundamental facts in it are. As well as what in fact happens, though, we also want an account of what can and cannot happen. We also want to understand how it can be true that certain things would happen if conditions were somewhat different. Questions about what could happen and what must happen, about what is necessary and contingent, about what is possible or impossible, are all called modal questions. (The terminology dates back to the medievals, who thought necessity and possibility were modes of sentences or propositions.) Philosophers increasingly came to recognize the importance of questions about necessity or possibility, or modality (as the subject is sometimes called) in the second half of the twentieth century. One reason for this is the role that modal questions seem to play in a host of other philosophical puzzles. One set of puzzles involves a family of concepts, including causation, laws of nature, objective chances, dispositions and powers and conditional statements. Questions about what causes what are intimately linked to questions of what must happen if something else does, and also to questions of what outcomes can be brought about by certain causes. Questions about the laws of nature seem to concern what must be true, as opposed to what happens to be true as an accidental matter. Chances or probabilities sometimes seem to be weighted possibilities: the more probable something is, the greater the possibility that it will occur.