These claims are really plausible:
- I exist because I was caused by my parents.
- My having been caused by my parents is a fact about me.
- My existence is explanatorily prior to all other facts about me.
- There are no loops of explanatory priority.
But actually there is no contradiction. To get the claim that my existence is explanatorily prior to my being caused out of (3), we need to add the premise that my being caused is a different fact about me from my existing. But why add a premise that makes for a contradiction? We should instead conclude that the fact of my existence is the same fact as my being caused by my parents.
But if it's the same fact, then we have an interesting ontological conclusion: My existing is my being caused by my parents (and presumably by all the other causes cooperating with them, including especially God). I've argued for something like this conclusion here, but this is a much neater argument.
There may be another corollary. It seems that my esse, my existence, is modally essential to me--I couldn't exist with a different esse. But if my esse is my being caused by my parents, then I couldn't have had other parents.
Objection 1: We should restrict (3) to facts about the present time. But my having been caused by my parents isn't like that.
Response: Run the argument in the first moment of my existence (assuming there is one; if not, run it for some creature which has a first moment of existence; presumably if the ontological thesis I am arguing for is true for some creature, it's true for them all).
Objection 2: If my existing is the same as my being caused by my parents, how can (1) be true: isn't (1), then, a claim that I exist because I exist?
Response: Even if the fact (or state of affairs or event--there are multiple ways to formulate the argument) of my existence is the same as the fact of my being caused by my parents, the proposition that I exist is not the same as the proposition that I am caused by my parents.