A proposition that can’t be acted upon must be false, or even meaningless. So its contradiction must be true. Thus you can’t think that you can’t think, e.g.; so you can think, period full stop.
The corollary is that if you cannot avoid acting as if a proposition is true, then it must be true. You must at every moment act, willy nilly; so it is true that you can act. Your agency is real. There is literally no way around this operational presupposition. There is no way for us to be, except by an implicit presupposition of its truth. And the only way for us not to be – namely, suicide – is a way that, again, implicitly presupposes its truth. You can’t kill yourself if you can’t act. You can kill yourself. So you can act. QED.
Likewise, you cannot but know that you can know, cannot but treat the world as real, cannot but treat other persons as such, and so forth. So it has to be true that you can think about and know a real world with real people in it. Which is good, because we have no alternative but to do just that.
So all silly philosophical notions – as materialism, nominalism, determinism, positivism, nihilism, skepticism, acosmism, and the like – devour themselves in their very consideration. It is impossible to think about them other than by implicitly repudiating them.
This will be more controversial, perhaps, but the same thing goes for atheism. You can’t aver that God does not exist other than by invoking the concept of God. But the concept of God, if it is coherent – which it is – entails his necessity. You literally cannot think about God, properly so called, other than by presupposing his necessary existence. So you can’t assert that God, properly so called, does not exist, except by virtue of a prior implicit assertion that he does.
To think “God” *just is* to think “that which necessarily is.”
Excursus: Tace for the nonce, of course, on the proper meaning of “is” as it pertains to God. It doesn’t mean what it means in respect to any other thing that is. But it doesn’t mean less; on the contrary, it means ineffably *more.*
To think that God might not exist, then, is to think that something other than God, properly so called, might not exist. It is in other words to think about something other than God. It is to miss the point of theism altogether. Atheism as such, then, departs categorically from consideration of God. It descends by definition into consideration of something categorically less than God; into consideration of gods like Thor or of a Flying Spaghetti Monster or of some other such thing that is *nothing like God.*
Alright, let’s cash this out. To be an atheist is to assert that the God who necessarily exists does not exist; or else, it is to believe that the Flying Spaghetti Monster (or something like it) – but, *not* God – does not exist. To be an atheist is, in other words, either to be an implicit presuppositional theist, and thus to engage in a fatal retortion, in which you can’t say that God does not exist except by saying that he necessarily does exist; or it is to misconstrue the topic under discussion.
My experience with atheist interlocutors suggests that most will end up taking the latter course.
I know of course that there are lots of atheists out there who deny that atheism is an assertion of the nonexistence of God, and insist rather that it is more properly an admission that the atheist himself does not yet know whether or not there is a God.
But that won’t do. To think about God at all is to think about that which must necessarily exist. To think that, having thought about him, you might then need to adduce empirical evidence – or any other sort for that matter – for the proposition that what must necessarily exist must necessarily exist, is to descend into abject stultification.
We cannot but think that God, properly so called, necessarily exists; for, his necessary existence is entailed by definition in his ultimacy. We cannot but think that God necessarily exists. So God necessarily exists.