Abstract

Quine's formal challenge to quantified modal logic involves the dual problems of referential opacity and extensional transparency. Quine's position is that the modal logician is faced with an inescapable dilemma: modal logic is either referentially opaque or extensionally transparent, and, hence, either "quantification into" modal contexts is illegitimate or the distinctions between the necessary, the possible and the actual collapse. Quine himself was convinced that the first horn of the dilemma is true, that modal logic is referentially opaque; however, I argue that neither horn of the dilemma is true in any significant sense. ;Basically, Quine's error lies in his confusion of the two principles of substitutivity of identity and indiscernibility of identicals. However, given an appropriate understanding of the description, the two principles can be seen to be distinct, for the principle of substitutivity fails to take account of the complexity of singular terms such as definite descriptions. This error plays an essential role in each of Quine's arguments. Thus, Quine's formal challenge to quantified modal logic can be met. ;Yet, despite this formal failure, Quine's insight regarding another relevant issue is correct, for interpreted quantified modal logic is committed to "Aristotelian Essentialism" in an important sense. Thus, the focus of the problem of quantified modal logic must shift from the formal difficulties of referential opacity and extensional opacity to the issue of the intelligibility of the metaphysics underlying quantified modal logic