Is there such a thing as free will, or is our every choice predetermined? Here's a thought experiment:
Suppose I think that I might want to eat some ice cream. I go to the freezer compartment and pull out an unopened half-gallon of vanilla ice cream and an unopened half-gallon of chocolate ice cream. I can't decide between vanilla, chocolate, some of each, or none. I ask a friend to decide for me by using his random-number generator, according to rules of his creation. He chooses the following rules:
- If the random number begins in an odd digit and ends in an odd digit, I will eat vanilla.
- If the random number begins in an even digit and ends in an even digit, I will eat chocolate.
- If the random number begins in an odd digit and ends in an even digit, I will eat some of each flavor.
- If the random number begins in an even digit and ends in an odd digit, I will not eat ice cream.
Suppose that the number generated by my friend begins in an even digit and ends in an even digit: the choice is chocolate. I act accordingly.I call that free will.
I didn't inevitably choose chocolate because of events that led to the present state of my body's chemistry, which might otherwise have dictated my choice. That is, I broke any link between my past and my choice about a future action.
I suspect that our brains are constructed in such a way as to produce the same kind of result in many situations, though certainly not in all situations. That is, we have within us the equivalent of an impartial friend and an (informed) decision-making routine, which together enable us to exercise something we can call free will.
UPDATE: Sir James Jeans, near the end of Physics and Philosphy (1943), says this:
The classical physics seemed to bolt and bar the door leading to any sort of freedom of the will; the new [quantum] physics hardly does this; it almost seems to suggest that the door may be unlocked -- if only we could find the handle. The old physics showed us a universe which looked more like a prison than a dwelling-place. The new physics shows us a universe which looks as though it might conceivably form a suitable dwelling-place for free men, and not a mere shelter for brutes -- a home in which it may at least be possible for us to mould events to our deires and live lives of endeavour and achievement. (Dover edition, p. 216)Even if our future behavior is tightly linked to our past and present states of being -- and to events outside of us that have their roots in the past and present -- those linkages are so complex that they are safely beyond our comprehension and control.
If nothing else, we know that purposive human behavior can make a difference in the course of human events. Given that, and given how little we know about the complexities of existence, we might as well have free will.