Compatibilism is belief in actions that are both free and determined. Usually, one hears such phrases as "what I will to do, I must do" (I think Hume phrases it something like this) or "I am free to act according to my nature." The idea is that human beings have determinate natures and they act as their natures determine. They are free because nothing outside determines their actions.
Theories that posit a more robust freedom of the will are called "libertarian" (no relation to the political theory referred to in my tagline). Usually one hears phrases like "I am free because I might have done otherwise." (Of course, if actions were completely random, that wouldn't be freedom either, so I believe that libertarians must posit a type of action that is neither free nor determined.)
Foreknowledge is often considered to be a problem for the latter type of free will. In order for it to be possible for there to be knowledge of something, there must be a fact of the matter about it, and even the existence of such a fact (a fact about what I will choose which is already the case before I choose it) has often been thought problematic. This is often solved by simply saying something about how it is my future choice that is the truth-maker for this fact. In an eternalist framework (one that views all times as existing equally, and does not give a priveleged position to the present), it seems unproblematic that my future choice should make something true now. In fact, if we take relativity seriously enough, then it isn't really that different from, for instance, a choice I made while in Greece making some fact true here in the U.S. Certainly that is unproblematic!
A further objection arises in terms of someone actually knowing the truth-value of the fact (especially me knowing what choice I will make before I will make it, through some other means than deciding). It is thought that this will interfere with free will since someone knowing the fact "pins it down" as it were. However, if eternalism is true, the fact is already "pinned down" - that future time exists, and in that future time, I make the choice. Still, it seems that my knowledge could interfere with my freedom in this sort of case.
The foreknowledge of God is considered to be a special case which is somewhat easier to get out of: since God exists atemporally, he witnesses all moments simultaneously, and so he simply observes me making my future choices. But why should foreknowledge had by an agent within time be any more problematic than this?
Consider the "Grandfather Paradox" as a famous example. Here is David Lewis's formulation of the problem:
Consider Tim. He detests his grandfather, whose success in the munitions trade built the family fortuen that paid for Tim's time machine. Tim would like ntohing so much as to kill Grandfather, but alas he is too late. Grandfather died in his bed in 1957, while Tim was a young boy. But when Tim has built his time machine and traveled to 1920, suddenly he realizes that he is not too late after all. He buys a rifle; he spends long hours in target practice; he shadows Grandfather to learn the route of his daily walk to the munitions works; he rents a room along the route; and there he lurks, one winter day in 1921, rifle loaded, hate in his heart, as Grandfather walks closer, closer,....
- David Lewis, "The Paradoxes of Time Travel," American Philosophical Quarterly, 13
Perhaps the concern is something like this: suppose that Tim goes through the same reasoning we have just gone through, and determines that he didn't and won't kill Grandfather, and therefore doesn't try. Further suppose that we have the correct theory of truth-conditions for counterfactuals (including counterfactuals of freedom - suppose that these have truth-values), and, on this theory, the statement "if Tim had tried to kill Grandfather, he would have succeeded" is true. Then we seem to have at best a case of circular causation, and maybe even worse difficulties. Consider an explanation of why Grandfather didn't die. It might go something like "although Tim could have killed Grandfather had he tried, he did not attempt to kill Grandfather because he knew that he didn't kill Grandfather." Or we could condense it into the even worse sentence "Tim chose not to kill Grandfather because he knew that he didn't kill Grandfather." Let C represent "Tim chose not to kill Grandfather" and D represent "Tim didn't kill Grandfather." It is now the case that (according to libertarians) C is the truth-maker of D, but D is the reason for C. What a headache!
But is this really worse than circular causation? I'm not sure. And, honestly, circular causation doesn't bother me too much anyway. It's not any worse than an infinite chain of causation, both of which are fine if there is a sufficient reason outside the chain or circle for why the chain or circle is. However, in this case, it doesn't seem that God can be invoked as the reason, because then we would no longer have libertarian free will (either God would be the truth-maker for C and not Tim alone or, worse, God would be the truth-maker of D and not Tim's free choice).
Might libertarians escape through their denial of psychological determinism? That is, Tim's knowledge that he didn't and won't kill Grandfather doesn't actually prevent him from trying in any deterministic way, so perhaps he might still have tried, and succeeded, and then it would have been eternally true that Tim killed Grandfather - but then Tim would not have been born, would not have built a time machine, would not have killed Grandfather, etc. Perhaps, however, this is only an argument against (one dimensional) time travel. Perhaps if we remove the causal problem it will work.
However, libertarians don't want to deny that our beliefs, etc., influence our choices, so it seems that we would still have a circularity problem. Perhaps a degree of uncertainty solves the problem. That is, I think it is very unlikely - say, probability .05 - that I will ever audition to be a television actor. I think this based on my plans, decisions, etc., in the present. But suppose I somehow gain additional information that makes it very likely - but not certain - that I will audition as a television actor in the future. It seems to me that whether this help will depend on its source. If someone I believe to be very skilled in such matters tells me, based on extensive psycho-analysis, that I am highly likely to make such a choice, this is not very problematic. But if I get a message from the future, that may be more problematic. We may have the circularity problem again.
But consider Tim once more. Suppose Grandfather is not his grandfather, but my great-grandfather (my grandfather not having been born in 1921). Tim doesn't know that he didn't and won't kill Grandfather, but I do. This doesn't seem to suffer from the same problem of explanatory regress. However, we must then ask the question of whether I am free to tell Tim what I know.
These are serious problems, but I'm not convinced they are unsolvable. We are walking along our epistemic boundaries here, and mind-bending difficulties here and there are to be expected.
The reason I am interested in these problems, is that it seems like detailed knowledge of brain states, etc., might provide the kind of information that runs into these difficulties. Then again, it could simply be that between the Uncertainty Principle of quantum mechanics and the limits of our ability to gather and process information (we can only know so much about a person's present brain states, and to then figure out what stimulus the person will experience in enough detail to make predictions may be impossible for humans) may make it impossible for us to reach this kind of knowledge. If there are no temporal beings capable of gathering and processing enough information to do this sort of thing, then the theoretical possibility of such a thing is probably unproblematic.Posted by Kenny at February 24, 2007 1:47 PM
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