This is a response to a challenge by Scott Adams on why rational people believe in free will given the evidence against it.
Personally I think that it is possible to both have free will (in one important and slightly restricted sense) and yet have a brain function that is deterministic. What do I mean?
It has been shown many times that when we make decisions we generally make the decision before we are aware of it. There is an important experiment that shows that when we are allowed to press a button at any time it is actually possible to read the potential for "I will press the button" grow until we actually do it. We think we've made the decision at the instant we press the button, but actually that decision has been brewing for quite some time and somebody with the right equipment who knows what to look for will know when we are going to press that button before we do.
The point here is that in a given situation or response is pre-programmed. Somewhere deep in our brain the endless round of will I? or won't I? has been building to that yes! moment. And of course the same thing happens all the time. We don't really think about conversations whilst we're having them. They just happen. We say things without really being aware that we're on about. All of these things are already determined in the same way that a computer is programmed. On hearing or seeing something we're likely to say a certain thing. Whatever that thing is that's said it isn't said of our free will—it just happened.
But, after that situation has passed we are able to comtemplate on our decision and what we said. We think and we cogitate and if we think we did the right thing then we carry on. If, on the other hand, we think we did something wrong then we change our bahaviour for next time—we do something different.
So, we don't have free will when we're busy doing things. All of these things we do is a consequence of the way our brains are wired (or programmed), but after that situation we have the option of changing that wiring, we can re-program ourselves to do it differently next time.
Now, one could of course argue that this contemplatory re-programming task is also done in a deterministic way and thus denies our free will. But I think it has a few extra, crucial, inputs that are important. First of all is our experience of the earlier decision and secondly is the reaction of others around us to that decision. Throw in a bit of randomness in the outcomes to what we do and the whole thing becomes so complex that the phrase free will is as good as any to describe it.
So, to recap, free will is an illusion in the restricted sense that what we do has already been determined by our brain's wiring. But the fact that we are able to look back and learn from our mistakes (and our accomplishments* [*And better yet those of people around us and in history.]) gives such a complex and un-predictable set of outcomes (still based on a personality which is the product of this internal programming) that we may as well call it free will as anything else. It's certainly free will in the sense that it's my contemplation and thinking about what I've done and seen that alters the way I program my brain to behave in the future.
Free will is both real and an illusion depending on how you look at it. Anything that complex certainly looks free to me though.