I was thinking about the short argument I gave here and was wondering if it could be turned into a positive argument for theism. I came up with this:

1. If God doesn’t exist, then our cognitive faculties arose from non-purposive processes.
2. No purposive system can arise from non-purposive processes.
3. Therefore, if God doesn’t exist, then our cognitive faculties are non-purposive.
4. Rationality is purposive.
5. Therefore, if God doesn’t exist we aren’t rational.
6. Therefore, atheism is self-defeating.

It seems promising. Although, I suspect I should read JP Moreland, Alvin Plantinga and Victor Reppert to get a better idea of the contemporary debate around this stuff. I think (4) is pretty solid (see the previous post for why), and I’m uncertain any atheist will disagree with (1), lest they open themselves up to Aquinas’ fifth way. So, presumably, (2) is the key premise. But this certainly does seem plausible.