Summary
Necessity and possibility
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Extract
Classes, worlds and hypergunk.
1. Testing the Possible
The question of what truths are necessary in the broadest possible sense is a difficult one to answer, as is the question of what the limits are to what is possible. (Most people would see these two questions as different sides of the same coin, of course, since many think the question of what is possible is just the question of what is not necessarily ruled out). We have three general sorts of strategies for determining whether something is necessary (or possible). We can identify it in a class that we were previously sure was a class of things that are necessary--we might show it is a theorem of a logical system that we have confidence in, or that the sentence appears to be true simply in virtue of the meanings of the words, or that it is a true statement involving names or about natural kinds of the "necessary a posteriori" sort discussed by Kripke and Putnam, and there are perhaps other classes of claims which we are prepared to accept are necessary if true? Likewise, we might establish the possibility of something occurring by reference to a class of well-established or uncontroversial possibilities: e.g., we are inclined to think that it is possible (in the broadest sense) for an event to occur in the future if one of the same kind has occurred in the past. (2) A second sort of strategy is to appeal to a general theory of modality (a theory of possibility, necessity, counterfactuals, possible worlds, etc.). This can be useful both for questions about what is necessary and what is possible--such theories often have answers one way or the other about some difficult cases that we had little to say about pre-theoretically, or that we had mixed inclinations about. The advantages of having a systematic set of answers that have been justified in a non-haphazard way is one important reason for developing explicit theories, after all: though in many respects our theories of modality are much less well developed and supported than our theories of, for example, chemical composition or ancient history. The third strategy is to apply some rough-and-ready tests to a case to see whether it is genuinely possible: these tests include seeing whether one can prove a contradiction from complete descriptions of the case; whether the case can be described without obvious violence to the language, and perhaps whether the case is conceivable (or has a certain sort of conceivability, since presumably in most disputes about wha...See the full content of this document
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