As a young man at Oxford in the 1320s, Thomas Bradwardine wrote a treatise on Insolubles (self-referential paradoxes) which transformed the medievals' approach to these problems. He was, in the later words of Ralph Strode (a friend of Chaucer's) "that prince of modern natural philosophers who first came upon something worthwhile about the insolubles." The key to his solution is a closure condition on meaning: a proposition means (or signifies) everything that follows from what it means. Using this postulate, Bradwardine proves his main theorem: Every proposition signifying that it itself is not true, or false, also signifies that it is true and so is false. All the semantic paradoxes, the Liar, the postcard paradox, Curry's paradox, Yablo's paradox, the Knower paradox, Russell's propositional paradox, succumb to the power of this theorem.