Language

In this chapter we will consider the ways in which the notions of possibility and necessity, and related notions, are expressed in ordinary language. Ordinary usage will indicate the concepts used, and the interrelations between them. There are also sentences of English that pose considerable difficulties for translation to logics that use possible worlds semantics. At the same time, possible worlds can, in some cases, illuminate the meaning of the propositions expressed by such sentences. Above all, reasoning and arguments involving the notions of possibility and necessity are usually expressed in ordinary language.

We begin with the distinction, in ordinary language, between “possible for” and “possible that”. We then move on to consider some difficult cases. We consider whether the idea of possible worlds is effective in explaining the interrelationships between the concepts that surround possibility, correct reasoning and the validity of argument in ordinary discourse.

“Possible for” and “possible that”

“What's possible?” “What's impossible?” These questions are asked in context. In government the questioner might want to know what is economically possible. In business the questioner might want to know what is financially possible. In academia the questioner might want to know what is politically possible in the academic institution, or what is possible given the regulations for the degree. In physics the questioner might want to know what is physically possible. In chemistry the questioner might want to know what is chemically possible.