Having very recently started getting interested in philosophy, I'm still halfway through my first book (Think: A Compelling Introduction to Philosophy, by Simon Blackburn, as recommended in this question).
Before reading it, it was my belief that we acted according to free will, not bound by any deterministic rules (is this one 'type' of incompatibilism?). If I came upon a t-junction on a road, I could choose whether I went left, right or back. Yes, I had the notion that I would make that decision based upon every knowledge that I had acquired until that moment, thus being bound by that. I understood that my decision was bound to the way every one my my past experiences influenced my thinking and decision making process. But, despite these constraints, I possessed free-will, and I was free to choose down which road I decided to go. I had the impression something like this happened:
Here, the red dot represents a point in time where a decision was/is made. Also, the past was composed of several other ramifications such as this one, but here it can be represented as a straight line, considering that we would ignore all the choices I did not make.
However, after having read the book's chapter on Free Will, such a possibility is not even considered (or if it was, it was not clear to me). I took this easily, as I actually understand that it could be considered, as Blackburn puts it, 'bad philosophy'. This was clear to me, as soon as I read the first quote present on this chapter:
Again, if movement is always connected, new motions coming in from old in order fixed, if atoms never swerve and make beginning of motions that can break the bonds of fate and foil the infinite chain of cause and effect, what is the origin of this free will possessed by living creatures throughout the earth?
Lucretius, De Rerum Natura
Since we are indeed inserted in a physical world that responds to cause and effect, we must consider that we are too bound to this law. This makes it clear to me that determinism is very likely to 'be real' (as in be the 'thing' that really happens), since the past controls the present and the future, and we are not able to control the past, leaving us unable to control both present and future too (leaving us in control of nothing, basically). This would point toward incompatibilism, which I find easier to believe than its alternative.
So, Blackburn spends most of the chapter trying to reconcile free will with determinism, introducing the concept of compatibilism. This is where I have some trouble, for I really cannot see how the two concepts are conciliated.
He asks us to "think of the brain in 'software' terms, as having various 'modules'". Thus, we would have a 'scanner' module (which takes in information), a 'tree producer' module (that, according to what the 'scanner' says, produces options, similarly to the image I put above), an 'evaluator' module (which chooses which 'branch' of the tree is the best option) and a 'producer' module (which carries out the decision made by the 'evaluator'). This works very well, but (in my opinion) only when applied to the thinking I had before having accepted determinism (meaning the image above). I do not understand how the modules are not constrained by the same deterministic laws as everything else. Basically, this cartoon somewhat expresses how I feel:
So, throughout the chapter, the author refines a compatilist definition (that tries to reconcile the modules' free will and determinism), until he reaches this:
The subject acted freely if she could have done otherwise in the right sense. This means that she would have done otherwise if she had chosen differently and, under the impact of other true and available thoughts or considerations, she would have chosen differently. True and available thoughts and considerations are those that represent her situation accurately, and are ones that she could reasonably be expected to have taken into account.
So here I see a lot of could and would haves. This is where it really gets itchy, because the only thing I can take from this is that free will (according to these arguments) only exists in retrospective (or as an illusion in the moment when 'decisions' happen). Thus, I can perceive compatibilism as being viable only in retrospective, having my first image only as an illusion to a reality that could be represented as this:
In this possibility (reality?) there is no red dot, since I cannot see how decisions can actually be real.
The thing is that Blackburn then goes on to explain some scenarios that always end up with a lot of could and would haves, and I cannot see them as plausible. The impression I get is that compatibilism is built upon a lot of could and would haves, which cannot be proven (or at least his arguments did not seem, to me, to be able to do it).
Going back to my first example, I cannot see how the road I picked at the t-junction was ever my choice. Sure, my 'modules' are at work, analysing everything in the landscape, etc. so that I can make a decision. Sure it really seems to me that the results provided by such an analysis are the object of my own free will, but how can I ever really prove it, if in the basis of my thoughts I know that the physical world in which I (thus the modules) belong is bound by deterministic laws? What I mean is: upon analysis, I have the impression that I can choose where to go. In retrospective, I too am under the impression that I could have chosen differently. But how can I prove that I really could have chosen differently?
To sum up:
Before I could (or thought I could) see how people could act according to their own free will, unrestrained by any type of determinism, although bound to the conditions 'available' to them (however, this seems to be bad philosophy).
I now can see how we are bound to a deterministic physical world (ruled by the laws of cause and effect), where free will does not exist.
But I cannot understand the middle term between the two views. How can our notion of free choice not be restrained by our physical world, and thus bound by the laws of causation? How can free will and free choice exist in such a world?