Yes if you want to get into philosophical arguments only thing you really can prove is 'I think therefore I am.'
Actually, Descartes was wrong; you can't even prove that. The search for Truth is always a fool's errand. What you CAN do is see if things work out pragmatically in ways that are consistent with your hypotheses.
So far, the hypothesis that SPNG is on the up and up is working out quite well. As far as I'm concerned, it's "true" until proven otherwise.