When we say that a person has free will, we generally mean that he chooses his own actions and that, for every choice he makes, he could have chosen otherwise.
That “could have” is a little slippery. Usually we mean it in a counterfactual sense. When a falling stone just misses my head and I say that it could have hit me, I am not claiming that the motion of the stone was not deterministic; I mean simply that it would have hit me if conditions (my location, the direction of the wind, etc.) had been slightly different. When we say that a person could have chosen otherwise, it could likewise be interpreted to mean that would have chosen differently if certain conditions (such as his character, motives, or mood) had been slightly different — but proponents of free will generally mean something much stronger: that exactly the same person in exactly the same situation and the same mental state could have chosen otherwise — that precisely the same set of causes could just as easily have resulted in a different effect. The actions of a person who has free will are supposed to be impossible to predict even in principle, even by a psychic Laplace’s demon with complete information about the person’s character and mental state. But — and this is where the contradiction comes in — the actions are still seen as being decided by the person.
Basically, the claim that I have free will boils down to an assertion that both of the following propositions are true:
- I determine my actions.
- My actions are not determined.
Thus, the claim that I have free will is logically false. Free will is not just something which we happen not to have because the universe is deterministic; it is something fundamentally incoherent, which could not possibly exist in any conceivable universe.
When I made a similar argument in my post Free will: a problem for everyone, Bruce Charlton left the following comment:
Reason reasons-about only that which follows reason. Therefore if there was anything which did not follow reason, such a phenomenon would necessarily be invisible to reason.
So, the argument you make excludes the possibility of free will, from the initial assumptions. . . . reasoning excludes free will a priori – reason does not disprove free will.
Dr. Charlton goes on to compare reason’s exclusion of free will to the way science excludes miracles and the supernatural — not because it can disprove them, but precisely because it cannot disprove them, because they are deemed untestable and thus outside the domain of science.
Like science, reason supports some things, disproves others, and excludes still others from its domain. Simple propositions, for example, are excluded. Reason can’t tell you whether all men or mortal or whether Socrates is a man; it can only tell you that if those two propositions are true then it follows that Socrates is mortal. All our first principles and empirical facts come from outside reason and cannot be disproved by reason. What reason can disprove is a related set of propositions, and it does this by showing that the set is self-contradictory — but this is precisely what reason does with regard to free will, as I have shown above. If reducing something to a contradiction doesn’t count as disproving it, it’s hard to imagine what would qualify.
So, given that reason disproves free will, is there any respectable way to go on believing in free will anyway? Usually when you run into a contradiction, you can question the premises, but in this case the only two premises are part of the definition of free will; to reject either or both of the premises is to reject free will. (You can still use the term “free will” for whatever is left — that’s what most philosophers do — but you’d still be rejecting free will in the sense that most non-philosophers intuitively understand and believe in it.)
Since ditching the premises is out, the next option is to remember that deductive reason is infallible only in theory. Not everything that is logically true is obvious (that’s why math tests are hard), and an argument which looks airtight could still be fallacious in ways that escape our notice. Most people justifiably reject Zeno’s proof that motion is impossible even if they can’t find any logical flaw in his reasoning; the overwhelming empirical evidence that fleet-footed warriors can in fact catch tortoises overrides the claims of reason. In a similar way, and on similar empirical grounds, most scientists continue to treat both relativity and quantum theory as true even though they are known to be logically incompatible.
So, if there were strong empirical evidence that we do in fact have free will, it would be reasonable to dismiss the above disproof of it as a curious paradox which, like Zeno’s, must somehow be wrong even if we can’t understand how — if there were evidence. But in fact the only evidence we have for free will is summed up well by Spinoza (Ethics II, Prop. 35, Schol.):
Men are deceived in that they think themselves free, i.e., they think that, of their own free will, they can either do a thing or forbear doing it, an opinion which consists only in this, that they are conscious of their actions and ignorant of the causes by which they are determined. This, then, is their idea of freedom — that they do not know any cause of their actions.