A friend of mine showed me this logical “proof”, and I’ve had little luck finding where exactly an illegal step is made. Of course, reasoning like this can be used to prove any proposition whatsoever. Proving the existence of God is just for dramatic effect.

Let S be the sentence

[ul]*If S is true, then God exists.*[/ul]

Obviously, if we can show that S is true, then we will have shown that God exists. Thus we proceed to prove S. Since S is a conditional statement, we do this by assuming the antecedent, and then deriving the consequent.

Assume the antecedent; that is, suppose that

[ul]*S is true*[/ul]

is true. Then,

[ul]*If S is true, then God exists*[/ul]

is true. Thus we have that both

[ul]*If S is true, then God exists*[/ul]

and

[ul]*S is true*[/ul]

are true, so, by *modus ponens*,

[ul]*God exists*[/ul]

is true. This completes the proof that S is true. As already mentioned, this proves that God exists.

Any thoughts on this?