I have an argument regarding the validity of rationalism in a universe without non-deterministic free will.

If human being's theories, thoughts and ultimate conclusions are inevitable, (bound by determinism), then isn't it logically invalid for us to assign the term "rational" or "true" to any of our conclusions being that they were inevitable regardless of their rationality or truth. There would be no test that I would have been free to perform that could have allowed me to distinguish which of my inevitable conclusions were "true" or "not "true" or "rational" or merely "apparently rational".

It seems to me that inability to have believed otherwise is the highest description that can be made of a belief or conclusion, and that adding the un-testable term "rational" or "true" on top of the term "'inevitable" is logically invalid.

This would suggest that the term "rational belief" is invalid in a real world where all beliefs were inevitable.

We could possibly extend the argument I have made to say that if one person believes that they lack free will, then they can never rationally prove that anyone else lacks free will because the first person would have to admit that they may be incapable of having a belief that could have been otherwise, even if it was false.

  • But if our mind is "bound by determinism", then all humans would share the same beliefs and this also with respect to e.g. scientific theories... Commented Dec 10, 2021 at 18:05
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    I don't agree this must be so. Different human beings cold come to different inevitable conclusive beliefs. Commented Dec 10, 2021 at 21:43
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    I don't see how it follows. Can we not imagine a rational computer program, which say computes the hypotenuse of a triangle based on reasoning and yet is provably deterministic? Why do you think that free-will is required for rational thought?
    – Ewan
    Commented Dec 10, 2021 at 22:42
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    No. Beliefs are rational when they are consistent with available evidence and logic. Determinism makes what they are inevitable, but that does not prevent them from still being rational, sometimes or all the time. And if they are inevitably so then so much the better.
    – Conifold
    Commented Dec 11, 2021 at 4:19
  • You said: "There would be no test that I would have been free to perform that could have allowed me to distinguish which of my inevitable conclusions were 'true' or 'not 'true' or 'rational' or merely 'apparently rational.'" And what test could you perform is you did have non-deterministic free will?
    – Chelonian
    Commented Dec 12, 2021 at 22:21

1 Answer 1


I have seen the meme, but I don't understand the logic behind it. For me "rationality" is a testable property of a belief or statement.

How the belief originated, through free will, random generation or supernaturally is immaterial. As long as you can state the belief in the form

"given X then due to logic Y, conclusion Z follows"

Then it is rational, or a rationally held belief. Even if it's a supernatural belief such as: "Because god is good, and it would be bad for good deeds to be unrewarded, heaven must exist." Its still rational, because you have used reasoning to determine your conclusion.

Obviously if you still hold that Z is true after X or Y is shown to be false, then you are holding the belief irrationally.

If you hold Z to be true because it can be experienced, then its empirically held

If you hold Z to be true without reasoning, then its mysticism

So if you state something along the lines of:

"Given that animal have no free will, humans are not qualitatively different from other animals and things that are same are the same, humans don't have free will."

It's rational.

Now we can argue about the premise, whether animals have free will, or whether humans are qualitatively different from animals, the logic, whether things that are the same are the same and if it applies here. But that's the nature of a rational belief, you can argue about the truth of the conclusion based on reasoning rather than simple belief or experience.

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