Smurf said:
Fallicious argument. In order to think you first have to exist so that sentence is really saying "I exist, therefore I exist". That's begging the question.
If you take 'I think, therefore I exist', or 'P | Q', as an argument with 'P' as the premise and 'Q' as the conclusion, it certainly can't be circular because it isn't valid. However, if you add the premise 'P -> Q' (P implies Q), as you did in asserting that in order to think you first have to exist, it becomes an instance of Modus Ponens, '(P -> Q), P | Q', which isn't circular. You are correct, in a way, that '(P -> Q), P | Q' and 'Q | Q' are saying the same thing in that they are both valid arguments and have corresponding tautologies and theorems in classical logic. '(P -> Q), P | Q' becomes '(((P -> Q) & P) -> Q)' and 'Q | Q' becomes '(Q -> Q)'. In the same way, 'P | Q' corresponds to '(P -> Q)', which is what I had always thought he was asserting. But it seems he was just saying that 'Q' is a performative tautology, i.e., that 'I exist' is always true when the thing that 'I' refers to asserts that 'I exist' is true. Makes me wonder what kinds of things can make assertions. I mean, my printer doesn't make an assertion when it prints 'I exist'... or does it? hmmm...
Um, and I might incur the wrath of the stupid joke gods, but that joke seems to rely on the fallacy of denying the antecedent, '(P -> Q), ~P | ~Q'. Or maybe that
was the joke. hmmm...
Now, if he had said 'I do not exist'...

Yeah. Good stuff.