Two Logical arguments in Comic Strips

The sensible one is a fallacy, the crazy one is valid

Garfield tries to use modus tollens as a Reductio ad Absurdum, but he makes a logical error, confusing John’s claim of necessity for a claim of sufficiency. Even if John’s arrival was necessary for an event to be a party, that doesn’t imply that his arrival is sufficient to make an event a party. Garfield’s inference would have worked only if…