Catch-22 did not exist, he was positive of that, but it made no difference. What did matter was that everyone thought it existed, and that was much worse, for there was no object or text to ridicule or refute, to accuse, criticize, attack, amend, hate, revile, spit at, rip to shreds, trample upon or burn up. (39.49)
It is nonsensical to say something does not exist but then does. However, Yossarian has a point here. Only to the extent that people believe in the twisted logic of Catch-22 does it actually exist and manifest its strange consequences on everyone. The tragic truth is that if the collective did not believe in Catch-22, it would not exist.