- If I am responsible for an event E, then I am responsible for at least one of the causes of E. (Premise)
- There are no infinite regresses or circles among the events I am responsible for. (Premise)
- Therefore, any event E for which I am responsible has among its antecedents a cause that I am responsible for and which is not an event. (By 1 and 2)
- All causes are either events or agents. (Premise)
- Therefore, any event E for which I am responsible has among its antecedents an agent that I am responsible for. (By 3 and 4)
- Therefore, if I am responsible for any event, agent causation occurs.
I think the argument is unsound because (4) is false. Causes can be events or substances. (Actually, I think only substances, but the weaker claim is all I need.) With this substitution, I get the conclusion that substance causation has occurs if I am responsible for any event. But then when we examine the substances I am responsible for, I think we will eventually get another regress. For substances other than myself, such as my dog (if I have any), I am responsible for only because I took on that responsibility. To avoid regress, I must arrive at a substance that I innately have responsibility for. And that's myself. Hence, there there is an agent who is a substance cause (namely I myself), and an agent who is a substance cause is an agent cause.
The equivocation is in (1), in that I am differently responsible for myself and for events. Maybe it's better to call it an argument from a disjunctive notion of responsibility rather than an equivocating argument.