Quine's objections to modal logic 3 - extensionality and intensionality

For his entire philosophical career, Quine was a confirmed defender of extensionality. In this video, I explain what this means and why it lead to skepticism about modal logic.

At around 4:20, I suggest picking up an intro to phil of language for more info on the extensions of sentences. A good intro is Morris's "An Introduction to the Philosophy of Language"; chapter 2 deals with Frege's account. Morris's book also provides, in chapter 6, an overview of the issues we'll be discussing in this series.

Regarding my comment at 13:18 that violations of extensionality are okay in the case of beliefs: in fact, Quine wasn't happy with these, either. Some of Quine's work on propositional attitudes (propositional attitudes are a kind of mental state, which we express using a verb followed by a "that": "Frank believes that...", "Frank hopes that...", "Frank desires that..." and so on) is very similar to his work on modality. See, for example, his paper "Quantifiers and Propositional Attitudes". An accessible introduction to his views on propositional attitudes can be found in the Morris book, chapter 7.

(More generally, Quine's approach to mental entities is often considered an early precursor to the radical eliminativisms of Dennett, Stich, the Churchlands, et al.)

The point is just that violation of extensionality seems to be more acceptable for beliefs, which we all expect to be messy, than for a completed, naturalistic theory of the world, which we expect to be "pure" and well-defined and so on.

Видео Quine's objections to modal logic 3 - extensionality and intensionality канала Kane B