Taking care of business

This chapter has two purposes. First, it is a housekeeping chapter. In Chapter 1, I asserted that there is a close tie between necessity and apriority: it seems that all our knowledge of necessities is a priori. In this chapter I set out a framework for talking about necessity: possible-world semantics. I also discuss theories of propositions. I do so because in later chapters we appeal to the notion of a proposition quite often.

The second purpose of this chapter is to discuss further the relationship between necessity and the a priori, and I introduce another property that a priori beliefs are supposed to have: certainty. I present and discuss two famous arguments due to Saul Kripke that attempt to complicate the connection between apriority and necessity. One shows that there are necessities that we know a posteriori (i.e. empirically) and the other shows that there are contingent propositions that we know a priori. Neither of these arguments, I suggest, endanger the claim that a priori knowledge is intimately involved in all our knowledge of necessities. But both arguments are interesting and important, and force us to be careful about the link between apriority and necessity.

I then look at the link between the a priori and certainty. Traditionally, and according to some contemporary philosophers, since a priori justification does not require any input from “outside”, it must be certain.