* The episode "Not-So-Great Great-Great-Grampa". At first, it seems like the GrandfatherParadox moves like they normally do. But think about this: If Phil had never been born, he never would have travelled to the past and given Kyle the idea for the prank, meaning Kyle would have stayed at H. G. Wells, never gone to military school, and never met Petunia. Which means that Phil would have [[MindScrew never been born.]] [[FlatWhat What.]]
** There's a bit at the end where they mention that Petunia likes Kyle, creating a [[TrickedOutTime Stable time loop]]
*** I get that. The problem is that ''there's no way for the paradox to be possible in the first place.'' Either Phil doesn't get born, or... [[LogicBomb he doesn't get born.]] I'm okay with [[TimeyWimeyBall Timey Wimey Balls]], but this makes no sense.
**** No, see, [[StableTimeLoop there was no zero-th iteration]]. Phil gets born, and causes his own birth in the process of his existence. There is no "doesn't get born". It's like a MyOwnGrandpa situation, where everything had to be in place. The series isn't terribly consistent across the series as to whether they [[InSpiteOfANail change the past]] or [[StableTimeLoop already went back to our present]] (unless the expectation that they ''can'' undo their trip to the past, as in the time capsule episode, is their own misunderstanding), but this is a perfectly logical series of events ''within the episode'', from what I recall. Unless that's the episode where Phil fades like [[Film/BackToTheFuture Marty McFly]], in which case disregard everything I've said relative to the subject at hand.
** Just because it was ''that'' prank that got him into military school this time doesn't mean that he wouldn't have done another equally dangerous prank that got him there. So it's quite possible that if Phil didn't come, he would've just performed other pranks until he finally got sent to military school.