The topic is ontology, the study of being. Western ontology asks the questions concerning existence. The doctrine given called hylomorphism teaches that there is actuality, what is that which is in existence, and potentiality, what is a reference to potentially in existence, either the potential to be altogether, or the potential to be different than what you are.
I don't get it. Hylomorphism, actuality, potentiality, ... For me those are just a bunch of lofty words. I don't see how they apply to reality.
I admit that I also often don't understand how the technical words used in the doctrine of Buddhism apply to reality, what they really mean, etc. However, there I just have more faith that they do somehow and that others have understood it, since they are supposed to point to actual aspects of experience that are to be observed.
In this case, however, I don't see how "actuality", "potentiality" etc. point to something that is to be experienced.
Maybe for unenlightened persons like us it's a matter of faith to a great extent. I don't think that you can convince me of these notions. However if you would want to you should try to clarify how they are related to experience.
From this reasoning, which is very sound,
If you say so.
Aristotle and those who followed him, reasoned that in order for anything to be actually in existence, not just a particular version of us at a given moment, it had to have an ultimate source which is pure existence, with no admixture of potentiality, no possibility that it could be anything other than what it is.
You (or those philosophers and thinkers you refer to) speak very much in riddles to me.
In the Christian context we call this principle God. If you don't like that word for some reason, then the principle is also called pure actuality. The basic reasoning is that none of us have within ourselves to give rise to our own selves, that is, we are not self-caused. Therefore we are caused by another. Nowhere, however, within that chain of causes is there any explanation for existence itself, since all the causes are merely in process of actualizing what is potential. It is only outside of that causal chain that we come to an explanation, which Aristotle called Pure Actuality.
I can feel how such an idea can be emotionally appealing.
I don't see that it gives me any clear understanding.
So either pure actuality is the answer, or it isn't. That is the crux of the debate. But if one posits that it isn't pure actuality, then they need to have an explanation for why anything exists at all. I am just supplying to robust argument. I didn't come up with it, but I am convinced that it is sound and true.
Either 42 is the answer or it isn't. But if it isn't then this needs to be explained.
To me you seem to live very much in a hypoethetical platonic world which I admit I don't understand. I was never very fond of theoretical philosophy.
But let's get back to some point which I think I do understand partly and where our viewpoints diverge.
You posit the need for an ultimate cause and say that a viewpoint without an ultimate cause needs explanation. Furthermore you say that the Buddha never seemed to get beyond infinite regress.
One could turn that argument around and say that you did not get beyond the need for a first cause on which to fall back on. The Buddha admonished us not to go for a speculative search for such an ultimate security. That is how I understand it. We should purify our actions right where we are, because that is the only way out of suffering. And that is the reality we are confronted with.
Earlier you pointed out that the ultimate cause you are looking for is not necessarily meant to be temporal but rather functional. In the temporal sense I don't see what's wrong with infinite regress, and I gather you don't see it either (although it's not completely clear, would be nice if you could confirm or deny that). But in the functional sense the Buddha did point out an ultimate cause, namely avijja/ignorance/not seeing things as they are. If you are looking for an ultimate cause that is at the same time ultimate goodness then this is of course not a satisfying answer and that is the reason why you keep looking. But as others have pointed out such an idea holds no water, because existence does not seem to be ultimately good.
After all I don't really see what you are looking for other than a platonic idea. And the explanation that you claim is needed for not looking for such a platonic idea is just honesty and integrity: "But when one sees the origination of the world as it actually is with right discernment, 'non-existence' with reference to the world does not occur to one. When one sees the cessation of the world as it actually is with right discernment, 'existence' with reference to the world does not occur to one."
Now I have to do some university stuff and will hopefully not be participating in this debate anymore until tomorrow.