- Professor Marcus struck the right note when she represented me as suggesting that modern modal logic was conceived in sin: the sin of confusing use and mention. She rightly did not represent me as holding that modal logic requires confusion of use and mention. My point was a historical one, having to do with Russell's confusion of 'if-then' with 'implies'.
- Lewis founded modern modal logic, but Russell provoked him to it. For whereas there is much to be said for the material conditional as a version of 'if-then', there is nothing to be said for it as a version of 'implies'; and Russell called it implication, thus apparently leaving no place open for genuine deductive connections between sentences. Lewis moved to save the connections. But his way was not, as one could have wished, to sort out Russell's confusion of 'implies' with 'if-then'. Instead, preserving that confusion, he propounded a strict conditional and called it implication.
- It is logically possible to like modal logic without confusing use and mention. You could like it because, apparently at least, you can quantify into a modal context by a quantifier outside the modal context, whereas you obviously cannot coherently quantify into a mentioned sentence from outside the mention of it. Still, man is a sense-making animal, and as such he derives little comfort from quantifying into modal contexts that he does not think he understands. On this score, confusion of use and mention seems to have more than genetic significance for modal logic. It seems to be also a sustaining force, engendering an illusion of understanding.
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