The following is a standard form of argument, but I've been trying to get to what I think is the most easily defensible, and least open to counterexamples, principle to base it on:
- If x is responsible for an event E and E is causally necessitated without overdetermination, then x is responsible for at least one event causally upstream of E.
- Responsibility in an agent like us requires either (a) that the first event the agent is responsible for is overdetermined; or (b) causal determinism is false.
- Compatibilisms do not require overdetermination.
It would be nice if we could handle the overdetermination option more neatly. Here is one way to do it. Say that an event E is strongly causally necessitated provided that it is causally necessitated, and if it is overdetermined, then each of the sets of overdeterming causes causally necessitates it. For instance, E's being strongly causally necessitated rules out the hypothesis that E is overdetermined by A and B, where A causally necessitates E while B causes E without causally necessitating E. If causal determinism holds, then every non-initial event is strongly causally necessitated. Then, we can replace (1) with:
- If x is responsible for an event E and E is strongly causally necessitated, then x is responsible for at least one event causally upstream of E.