I found a classical incompatibilist argument that looks that this:

  1. If a person acts of her own free will, then she could have done otherwise

  2. If determinism is true, no one can do otherwise than one does.

  3. Therefore, if determinism is true, one cannot act of her own free will.

This argument seems sound to me, but I still don't feel like I'm convinced. Is there any way to reject this argument? In premise 2, for example, how exactly does the truth of determinism entail that one cannot do otherwise than what she does? Also, in refuting incompatibilism, does it imply that I have to be a compatibilist in doing so?

  • 3
    The argument is valid. Premise 1 rephrases libertarian definition of free will (freedom to act otherwise in the same circumstances). Compatibilists reject the definition, and hence the premise. Their definition is freedom to act according to one's own wishes, no coercion, see Compatibilism. That wishes can be predetermined does not phase them.
    – Conifold
    Oct 12, 2019 at 9:25
  • it may help you to agree with @Conifold to put 'free will' in quotes
    – user38026
    Oct 13, 2019 at 2:25
  • @Conifold , why not make your comment an answer? Your point about premise 1 is the key insight here.
    – Chelonian
    Jan 5, 2020 at 17:26

2 Answers 2


(I am an incompatibilist - libertarian free will and not determinism. ) Let me rephrase the arguments using modal logic. (If an action is a contingent action then it is possible that it occurred and possible that it not occurred. If an action is necessary then it is impossible that it did not occur.)

Premise 1: If one acts out of one's free will, then one's action is free.

Premise 2: If one's action is free, then one's action is contingent.

Preliminary Conclusion: If one acts out of one's free will, then one's action is contingent.

Premise 3: If determinism is true, then all actions are necessary.

Preliminary Conclusion: If determinism is true, then no one's action is contingent.

Preliminary Conclusion: If determinism is true, then no one acts out of one's free will.

Premises 1 and 2 are a definition of libertarian free will. Premise 3 is a definition of determinism. The argument is logically valid. If you are a compatibilist, then you will have a different definition of free will and disagree with Premises 1 and 2.

And no, one does not have to agree with a position to disagree with an argument against it. I hope this helps!

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    – J D
    Jan 1, 2020 at 21:48
  • +1 I have a feeling that Premise 2 (thus also 3) is vulnerable to objections relating to under-determinism and sufficient as opposed to necessary causation, but am unable to formulate one at the moment so it's just a suspicion.
    – user20253
    Jan 3, 2020 at 13:31

To answer your second question first, if determinism is 'true' then all physical processes and systems are predetermined. This would include all those electrical and chemical processes that occur within the human brain, including those that result in the epiphenomena that we identify as thought, will, and consciousness. Thus, if we think we are making a choice between 'A' and 'B,' then in fact we are subject to a set of fully deterministic processes that both determine the behavior we identify as a 'choice,' and determine that we will perceive that behavior (erroneously) as something which we could have done otherwise. We would have the same status as a computer that is programmed to flick switch A and then to say aloud "I, the computer, have chosen to flick switch A."

This 'incompatibilist' argument is valid, and we cannot get around it without discarding the concept of free will or discarding the concept of determinism.

To your last question... Well, I'll likely get in trouble for saying this, but speaking philosophically, compatibilism was never really sound theory. Libertarianism as a whole is drastically undertheorized, in part (I think) because it has a strong aspirational element: an intuition of the way the world should be that is highly prized but difficult to justify empirically. The main problem is that it is difficult to justify any conception of 'free will' without triggering reactions from people who are suspicious of metaphysical constructs. Libertarians consistently try to avoid such conflicts by ardently avoiding the question, but that only goes so far.

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