Is Determinism Compatible with Rationality?

I finished listening to this wide-ranging discussion between Justin Brierley and Alex O’Connor, which I had previously commented on here. Towards the end of the episode, they get into an interesting discussion on rationality and determinism. Brierley (a theist) wants to say that we can’t make sense of rational choice in a deterministic universe, while O’Connor (an atheist) says that we can — our rational choices would just be part of the deterministic chain. There’s a sense in which I think they’re both right, but I want to dig into this a bit deeper.

Consider having three choice-points: at the first choice-point, I choose option A, at the second I choose option B, and at the third I choose option C, for the sequence A–>B–>C.

Rational Processes

Now let’s say this unfolded in a rational manner. Perhaps C was the rational thing to do, based on A and B (and perhaps other factors as well). In other words, I reasoned my way to C (and to B as well, and to A before that).

Deterministic Processes

Now, if determinism is true, we want to say that A, B, and C were each determined by prior events. For C, that includes prior events A and B, and B’s prior events include A. If we rewound the tape, the sequence would be A–>B–>C every time. So actual counterfactuals are impossible; I couldn’t have chosen differently.

Reconciling Rationality and Determinism

So A–>B–>C was determined. What does it mean to say that it was also rational? We can still say that C was the rational, reasoned thing to do, based on prior events. But this just amounts to recognizing a pattern in the sequence A–>B–>C; specifically, recognizing that the sequence unfolds in a rational way. And in that sense, rationality has no force. By no force, I mean that since it only amounts to the recognition of a particular pattern within a determined process, it is superfluous. We could not recognize the pattern, and it would not change anything. Our awareness of rationality doesn’t seem to do anything.

But rationality/reason seems to be one thing we cannot discard, as we would have to use reason to argue against it. There doesn’t seem to be any coherent way of making rationality superfluous or unnecessary.

Is Rationality Baked In?

Then how can we make sense of the fact that A–>B–>C unfolded in a rational way? If we want to say the sequence was determined, and that we couldn’t chosen differently, then it seems we are forced to conclude that the determined process had rationality “baked in” from the beginning. For some people, that idea might sound like it’s pointing to theism, but I don’t think that’s necessarily the case. Consider the Stoic idea of the Logos, and the universe being fundamentally rational. I don’t think we necessarily need libertarian free will, as Brierley does (and I’m not even sure what that kind of free will would look like), but I do think we need to recognize a fundamental rational nature of the cosmos.

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