 But Marsilius rejects the rather simple-minded proof that we noted Buridan and Albert give that every proposition asserts or signifies its own truth. For that proof turned on the assumption that every affirmative (resp. negative) proposition is true if its subject and predicate supposit (resp. don’t supposit) for the same thing, by the definition of truth. But insolubles are an immediate counterexample to this. As just noted, ‘This proposition is false’ is false (since it falsifies itself), and so its subject and predicate do supposit for the same thing. Indeed, ‘This is false’ says that ‘This is false’ is false (rather in the way Gregory’s second mental proposition said that the first mental proposition was false) and so, in saying that it’s false that it’s false, its formal signification is that it’s true. It’s implicitly contradictory and so false. 