12 - Modality
from Part III
The place of modality in a priori knowledge
The problem of justifying our beliefs about what is possible or necessary has been a recurring theme for us since Chapter 2. One of the central reasons why people have postulated a priori knowledge is in order to deal with modal knowledge. In this chapter we face this problem directly using the resources that we developed in earlier chapters.
We have already briefly discussed the radical empiricists' view about modal knowledge in Chapter 6. By and large, they reject modal knowledge. Mill, for example, says:
Why are mathematics by almost all philosophers and, even those branches of natural philosophy which, through the medium of mathematics, have been converted into deductive sciences, considered to be independent of the evidence of experience and observation, and characterized as systems of Necessary Truth?
The answer I conceive to be, that this character of necessity, ascribed these truths of mathematics … is an illusion.( 1974: ch. V, §1)
This is just a simple rejection of necessity. But in Quine the matter is somewhat more subtle than this.
Quine distinguishes between three ways to interpret modal statements. He calls these “three degrees of modal involvement” ( 1976c). First, one might treat necessity as a predicate of sentences. This means we take the word “necessary” to indicate some property of a sentence. Quine thinks that this is legitimate.
- A Priori , pp. 189 - 204Publisher: Acumen PublishingPrint publication year: 2011