On Philosophical Demonstration for the Existence of God

Why isn't everybody convinced?

I take it that there are philosophical demonstrations for the existence of God, or if one prefers, philosophical “proofs.” (I develop one in The Best Argument for God).

Of course, the common pushback to this claim is that, if there were such demonstrations, then why isn’t everybody convinced of them?

This objection has some force — but only some.

Once we make clear what counts as a philosophical demonstration, it also becomes clear why they can fail to convince people. Aside, of course, from the fact that many people just do not understand them. Here I am restricting my attention to people who presumably do understand them and still reject them.

I take it that for an argument to count as a demonstration it must be valid and possessed of true premises that are publicly accessible or reliably decidable.

So, philosophical demonstrations can’t be launched from special scientific knowledge – their starting point must be accessible to everyone, that is, pertaining to some broad feature of reality. Aquinas’s 1^st Way, for example, launches from the experience of change – a feature accessible to everyone via common experience, even if not accepted by everyone (i.e., those that claim change is an illusion) – conjoined to the claim, which Thomists take to be reliably decidable, that there cannot be an infinite regress of derivative (or per se) causes.

And there’s the rub.

Demonstrations require a fair bit of shared knowledge or common assumption or both. So, they will not convince “total outsiders”, which is to say people who do not share such knowledge or assumption, however common, and because of this they always leave enough conceptual space for people to opt out of the demonstration if they are already, for whatever reason, opposed to the conclusion.

I don’t think these admissions make a demonstration any less demonstrative; they just restrict what we should expect from the project.