I remember a thread about determinism a little while ago that I posted in, but I'll post the same argument here because I think it's pretty much flawless.
Free will is impossible. Absolutely. This is for two reasons. Firstly, the determinism/indeterminism debate:
Determinism is either true or false. It is impossible to prove either way, but we know that it has to be either one or the other. So, in any given reality, determinism is either true or false.
If determinism is true, then free will is false. This is because if determinism is true then the natural laws that governed the universe are such that they have created my thoughts, mental state and actions such as they are, and so they could not be any other way. Even should I consciously decide to make a rational, free choice, I could not, objectively speaking, have chosen anything else, natural laws being as they are.
However...if determinism is false and indeterminism is true, then free will is STILL false. If determinism is false, then my thoughts, desires and whatever are the result of completely random events. Since it is impossible to be in control of random events, I can not be said to have free will, since free will implies some free control over my own thoughts.
So there you have it...despite the fact that it's impossible to prove determinism, it doesn't matter. Whatever the case in our reality, either determinism or indeterminism is true, and both of these scenarios are incompatible with free will.
Furthermore...Galen Strawson has argued that the above discussion is irrelevant because free will is a logically incoherent and hence impossible concept.
Essentially, Strawson argues that free will is impossible because it leads to an unsolvable infinite regress in causality.
Free will requires that I cause my own mental state (from which my thoughts and actions come). My mental state at time 1 comes from my mental state at time -1. Which comes from my mental state at time -2. And so on back down into infinity to when I was born.
Essentially, free will requires that you cause yourself, which is impossible. You can not exist before your very first mental state in order to cause it. So free will is an incoherent and hence impossible concept.
So there you have it! Free will is incompatible with determinism, indeterminism, and itself! Sorted.
