Until very recently (the last hour!) I thought the following was quite a good model of what typically happens when a normal human agent x freely chooses between actions A and B: There are worlds wA and wB and a time t such that
- wA and wB coincide at all times earlier than t;[note 1]
- wA and wB have the same laws, and x is a normally functioning agent in both worlds in respect of the decision between A and B; and
- At all times later than t, it is true at wA that x has already freely chosen A, and it is true at those times at wB that x has already freely chosen B.
It is, I think, prima facie plausible, at least to libertarians, that at least some normal human choices satisfy the Symmetric Forking Model.
However, it now seems to me that the following three propositions are incompatible (though we may need to tweak them slightly to get this result—I am just sketching this):
- The Symmetric Forking Model holds of some normal human's choice.
- There is a certain tiny but positive amount of time e such that a normal human cannot be aware of distinctions between events where the person gets to observe the distinction for an amount of time less than or equal to e.
- Necessarily, if one has freely chosen A, then one was aware of the choice of A as a choice of A.
Why are these incompatible? Well, start with the Symmetric Forking Model and form worlds w*A and w*B which coincide with wA and wB, respectively, up to time t+e, but where our agent x is miraculously made unconscious at time t+e. Then, by (5) (with a bit of handwaving), the agent in w*A cannot be aware of having chosen A and the agent in w*B cannot be aware of having chosen B. For the agent does not get to observe the difference between choosing A and choosing B before t, since the two worlds coincide up to t, and hence only gets to observe the difference between t and t+e, which by (5) will not be enough.
The plausibility of (5) and (6) is enough to make me have serious doubts about (4). On the other hand, I can also see how the plausibility of (4) might be seen as casting doubt on (6). I am in fact suspicious of (6), so I do not think it is absurd to hold on to (4) but reject (6), if there is good reason to hold on to (4).
One might think that libertarianism commits one to (4). But that, I now think, is false. For one might have a case where the alternative to making at t the choice to do A is not making another choice, but temporizing and taking longer to make up one's mind.
I think it is an interesting challenge for a libertarian to construct a model of free choice compatible with (5) and (6). I have some somewhat inchoate ideas in this direction. But that may be fodder for another post.
[Edited to rename "Forking Model" to "Symmetric Forking Model", to distinguish this model from a different model that hopefully will figure in tomorrow's post.]