 Event-causal libertarians, of course, contend that self-determination requires more than nondeviant causation by agents’ reasons: for it is possible that agents’ actions in deterministic worlds are nondeviantly caused by apt mental states and events. Self-determination requires nondeterministic causation, in a nondeviant way, by an agent’s reasons. While historically many have thought that nondeterministic causation is impossible (Hobbes 1654 [1999], 1656 [1999]; Hume 1740 [1978], 1748 [1975]), with the advent of quantum physics and, from a very different direction, an influential essay by G.E.M. Anscombe (1971), it is now widely assumed that nondeterministic (or probabilistic) causation is possible. There are two importantly different ways to understand nondeterministic causation: as the causation of probability or as the probability of causation. Under the causation of probability model, a nondeterministic cause \(C\) causes (or causally contributes to) the objective probability of the outcome’s occurring rather than the outcome itself. On this account, \(S\)’s reasons do not cause his decision but there being a certain antecedent objective probability of its occurring, and the decision itself is uncaused. On the competing probability of causation model, a nondeterministic cause \(C\) causes the outcome of a nondeterministic process. Given that \(C\) is a nondeterministic cause of the outcome, it was possible given the exact same past and laws of nature that \(C\) not cause the outcome (perhaps because it was possible that some other event cause some other outcome)—the probability of this causal transaction’s occurring was less than \(1\). Given that event-causal libertarians maintain that self-determined actions, and thus free actions, must be caused, they are committed to the probability of causation model of nondeterministic causation (cf. Franklin 2018, 25–26). (We note that Balaguer [2010] is skeptical of the above distinction, and it is thus unclear whether he should best be classified as a non-causal or event-causal libertarian, though see Balaguer [2014] for evidence that it is best to treat him as a non-causalist.) Consequently, according to event-causal libertarians, when an agent \(S\) self-determines his choice \(\phi\), then \(S\)’s reasons \(r_1\) nondeterministically cause (in a nondeviant way) \(\phi\), and it was possible, given the past and laws, that \(r_1\) not have caused \(\phi\), but rather some of \(S\)’s other reasons \(r_2\) nondeterministically caused (in a nondeviant way) a different action \(\psi\).