Hi, I'm struggling to understand free will. I've been told that either of the following scenarios is commensurable with free will: (1) an omniscient being that knows all future events; (2) a block universe where future and past in some sense coexist with the present. But if free will is commensurable with these scenarios, would it be merely epiphemomenal? Would free will play any causative role if either of these conditions was true?

Your question suggests that you are thinking that free will must be something (e.g., a causal power) that is not a part of the rest of the universe, that it must be something that is (1) outside of the universe about which the omniscient being has complete knowledge, or (2) outside of the events that occur within the 'block' universe (an Einsteinian universe where there is no passage of time and the laws of nature describe the relationships between all the 'tenseless' events). If you think of free will that way, then yes, it seems like it cannot get a causal toe-hold on a universe that is already 'set in stone' like the block universe or one whose details are all already known by a god (who might be imagined outside the universe surveying it all at once). Free will, whatever it is supposed to be on this picture, would be cut out of the process, bypassed, epiphenomenal.

However, perhaps there is a better way to understand free will, one that neither has these consequences nor makes free will a mysterious causal entity that cannot really be understood at all. Free will is a label for a special subclass of events or processes within the universe (whether it's a block universe or a fully-known-by-god universe or neither). Free will picks out humans' uniquely well-developed capacities for imagining various ways we might act, evaluating those options, and deciding on the basis of these deliberations. Exercising those capacities makes crucial causal differences to what happens in the universe, especially by making a difference in how we act. In many cases, no other events are the 'causal source' of our actions, in that no events, more than our own deliberations, explain why we act one way rather than some other way. Our conscious mental activity, which is likely essential to these capacities, is also within not outside the universe.

Of course, on this view, our exercising our capacities for free will is an essential part of the universe, not distinct from it. As such, the way we actually exercise them will be 'set in stone' in the block universe--though not epiphenomenal for sure, since the events in the block universe would be quite different if our decisions were different. And the god would know how we actually exercise them, but that would not make them epiphenomenal. If anything, our making the decisions we do causes the god to know what she knows.

In case it's not clear, the response I'm outlining here is a compatibilist one, since it is a way of showing why free will is compatible with determinism (e.g., a block universe) or god's foreknowledge. But it's also meant to offer a sort of 'error theory' for why people might think free will is incompatible with these types of universes: they may be thinking that the only way to make a causal difference that matters in the universe is to act from outside of it and hence if that possibility is ruled out, they think they don't make any causal difference at all--their deliberations and decisions are bypassed or causally irrelevant. But there's no need to make that mistake. Once we come to understand how we (including our conscious minds) are a part of the rest of the universe, we'll be better able to see how our free will is a crucial causal component of our universe.

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