I suppose I’ll begin to reply to my friend’s comments. His input is in italics, my comments follow.
X is dependent on Y means that Y cannot exist without X. That X causes Y is not sufficient. Multiple entities might cause Y, and hence Y would not have a dependency on any particular entity.
I did not rule out the possibility of there being several causes for Y’s existence. Indeed, I alluded to the possibility. If Y cannot exist without X then surely X is a cause of Y’s existence. If X did not exist then Y would not.
There is no inherent contradiction in an object depending on itself for it’s existence. Indeed, every object is necessarily dependent on itself for it’s existence. X cannot exist without X, trivially. The question is whether every entity must have multiple dependencies.
I disagree. I think X depending on itself to exist is inherently contradictory. To say X cannot exist without X is entirely different from saying X is dependent on X. If X cannot exist unless it already exists then it will never come into existence.
There were more comments, including a challenge to define causality. I may return to these later but I think it digresses from the main argument a bit too much for the moment.