The Problem of Existence
To recap the discussion to this point, you [Father Tacelli] started out by stating "Fido exists." Against this you contrast some hypothetical First Cause, that is, an entity or force or being that by its nature is able to start that which we know, without itself succumbing to the problem of needing its own First Cause. Where Fido (and indeed, everything else in the known universe) is contingent on something else for its existence, the First Cause is not contingent. Thus, while Fido can be said to exist, the same cannot be said for the First Cause. I suspect that you will later argue that this First Cause is God, or at least a god.
In my first rebuttal and second rebuttal, I dealt with your opening arguments from the point of view that even given what you says about contingent beings, one still cannot logically arrive at the existence of God or a god.
There is another way of examining your opening argument, however, that deals with the issues surrounding existence and non-existence. Because in some ways such a discussion is much more fundamental to the overall discussion, it should not be overlooked.
Probably the briefest way of stating my disagreement with your position is this: We agree on the definition of existence, but we disagree on what can be said about something that, by definition, is said NOT to exist. I hold the position that if something is said not to exist, then there is nothing intelligible to be said about this thing. You apparently believe that if this thing that is said not to exist is God, then we can ascribe qualities and characteristics to this thing, even in the absence of any proof, or any possibility of proof.
read Tacelli’s response