Modality third grade

Abstract

Names and common nouns have played an especially prominent role in discussions o f modal logic. The reason is not hard to fred; for much of this discussion has centered on W.V. Quine's allegation that modal contexts contravene the substitutivity of identicals and that they are, therefore, referentially opaque and not subject to external quantification. To take the familiar example, while it is necessary that nine is greater than seven, it is not necessary that the number of planets is greater than seven despite the fact ( if it is a fact) that nine is the number of planets. The moral to be drawn, Quine tells us, is this: