Spurred by a chance encounter with Allan Wechsler, I just came up with a pair of sentences that have opposite truth values even though they are (formally) contrapositives: 1. If the premise of this implication does not contain the letter "p", then two is not even. 2. If two is even, then the premise of this implication contains the letter "p". Note that 1 is (vacuously) true whereas 2 is false. Of course there is no contradiction here, since "this implication" has different meanings in the two sentences. (Thanks, Allan, for teaching me the word "deictic" today!) Can anyone find a neater pair of sentences along these lines? My esthetic preference would be for eschewing tricks like referring to the letters that occur in different parts of the sentence. The sorts of sentences I would prefer would be things along the lines of "If the contrapositive of this sentence implies the inverse of this sentence, then either the premise of this sentence is true or the conclusion of this sentence is false." I've made unsuccessful attempts in the past to construct a true sentence of this kind whose formal contrapositive is false. Jim Propp