time travel vihvelin’s reply

the counterfactual coincidence argument 1. If time travel were possible, then the counterfactual coincidence principle is false. 2. The counterfactual coincidence principle isn’t false. 3. Time travel isn’t possible.

counterfactuals If I had tried to go home for lunch, then I would have slipped on a banana peel or had a last minute change of heart or… been prevented from going home for lunch in some other way. If I had tried to go home for lunch and not gone home for lunch, then I would have slipped on a banana peel or had a last minute change of heart or… been prevented from going home for lunch in some other way.

counterfactuals If I had tried to go back in time and kill myself as an infant and not killed myself as an infant, then I would have slipped on a banana peel or had a last minute change of heart or… been prevented from going home for lunch in some other way. If I had tried to go back in time and kill myself as an infant, then I would have slipped on a banana peel or had a last minute change of heart or… been prevented from going home for lunch in some other way.

vihvelin’s argument (C) Suzy can kill Baby Suzy. (S) If Suzy had tied to kill Baby Suzy, she would or at least might have succeeded. (F) If Suzy had tried to kill Baby Suzy, she would have failed.

vihvelin’s argument 1. If someone would always fail to do something if she tried to do it, then she cannot do it. 2. A time traveler would always fail to commit retro-suicide if she tried to do it. 3. [So] A time traveler cannot commit retro-suicide.

vihvelin’s revised argument 1. If someone would always fail to do something no matter what she did, then she cannot do it. 2. A time traveler would always fail to commit retro-suicide no matter what she did. 3. [So] A time traveler cannot commit retro-suicide.

counterfactuals Ryan would fail to run a five-minute mile if he tried. Ryan would fail to run a five-minute mile no matter what he did. …if he tried. …if he took a nap. …if he sat down and read a book. …if he devoted the next five years to rigorous training with Olympic-caliber runners and then tried.

counterfactuals Suzy would fail to kill Baby Suzy if she tried. Suzy would fail to kill Baby Suzy no matter what she did. …if she tried. …if she took a nap. …if she sat down and read a book. …if she shot her with a “miracle” bullet.

vihvelin’s revised argument 1. If someone would always fail to do something no matter what she did, then she cannot do it. 2. A time traveler would always fail to commit retro-suicide no matter what she did. 3. [So] A time traveler cannot commit retro-suicide.