Eddy Nahmias:

Determinism is sometimes presented to mean that the past and laws control us or that our actions are pre-determined, as if someone planned them. But it should not be anthropomorphized in these ways. The Big Bang did not plan our lives, and it didn’t really cause what we do in any useful sense of ‘cause’. Determinism should also not be confused with fatalism, the idea that certain things (like your actions, or Oedipus’ sleeping with his mom) will happen no matter what – that is, no matter what you want or try to do (or no matter what Oedipus tries to do to avoid his fate). Quite the opposite – determinism suggests that what happens in the future depends on what happens in the past and what we do in the present. Finally, determinism should not be confused with what I call bypassing – the idea that our conscious mental activity is not causally relevant to our decisions and actions. Determinism does not mean that our minds don’t matter.

So, what does determinism mean? In the philosophical debates, it is a specific thesis about the relations between events or states in the universe, as governed by laws of nature. It says that, holding fixed the laws of nature and the state of the universe at one time (e.g., the distant past), there is only one possible state of the universe at any other time (e.g., the future). As such, determinism does not mean that reductionism is true – i.e., that everything can be explained in terms of low-level physical events (such as interactions between quarks or neurons) – nor does it mean that epiphenomenalism is true – i.e., that our (conscious) mental states play no causal role in what we do. Some people worry that reductionism entails epiphenomenalism, and most people (rightly) worry that epiphenomenalism would threaten free will. But these are different heads of the monster, distinct from the (now-shrinking) head of determinism.

…I can’t rehearse these arguments here, but here’s just one quick thing to consider. Do we think that the truth of determinism would make it false to say, “That leaf [that just landed there] could have landed somewhere else”? I don’t think so. I think we think the leaf could have landed elsewhere, and we probably think that if it had, it would have been because something had been slightly different (e.g., strength of wind, time it broke off of tree, etc.). And those earlier differences were possible too. Determinism is entirely compatible with this analysis of ‘could have happened otherwise.’ It doesn’t make everything inevitable. Now, do we mean something different in kind (metaphysically different) when we say, “That student could have chosen a different paper topic”? Do we commit ourselves to the universe being indeterministic when we say or think such things about human choices? I doubt it. We do think that our choices involve lots of complex factors and capacities that tree leaves (and dogs and babies) don’t have.