For one, this isn't an ontological argument, this is a version of the cosmological argument.

I mean, I'm not even concerned about the truth or falsity of the conclusion of this argument. I posed this argument to you, and right away, we've started talking about ontological categories and what it means for something to exist. Have we not already started doing philosophy? Wasn't this supposed to be a purely scientific discussion?

> For one, this isn't an ontological argument, this is a version of the cosmological argument.

Potato, potahto.

> Have we not already started doing philosophy?

No. Establishing the meanings of words is part of science. You should read chapter 7 of David Deutsch's "The Fabric of Reality" and pay particular attention to the part where he says, "Languages are theories."

I mean, talking about what things exist, and what things don't, and what it means for something to exist are things that philosophers do as part of philosophy (specifically ontology). I suppose there's nothing wrong with Deutsch's characterization, I guess we can just call the philosophers who, in doing philosophy, discuss the meanings of words (like what it means to exist or, as Dennett and many other philosophers have, what it means to have free will, or all kinds of other terms) scientists who are actually doing science. If we use the terms this way, the academic discipline of philosophy seems perfectly justified since it's actually secretly scientific (they just don't know it themselves!).

But maybe more seriously (and hopefully more fruitfully), I should ask, according to Deutsch's/your characterization, what would count as doing philosophy as opposed to doing science? I would normally say "the things that academic philosophers do as part of their discipline", but it looks like that definition isn't going to stand.