The free-will intuition seems to be something along the lines of 'I could have chosen differently if I had wanted to'. That 'if I had wanted to' seems to be perfectly consistent with assuming that the person wouldn't have chosen any differently than they actually did if their purposes and motivations weren't sufficiently different. So free-will seems entirely consistent with causation and even with causal determinism taking place inside the chooser's head. In their brain and nervous system in other words. Not only does free-will seem to be consistent with that kind of determinism, it presupposes it. It's what ties the person's actions together with his/her will, purpose and motivation and makes human action something different, more goal-directed and purposeful, than seizures that merely cause the body to jerk around.
Yet the question remains of how much freedom there is within this freewill.
I would suggest none, and that "his/her will, purpose and motivation" are mere interpretations of the patterns of activity, but with no ability to change them from that which they are.
This does not mean that I can not appear to change it from one moment to the next, but that any apparent change is merely the outcome of a causal chain that adheres to the universal laws.
The proponents of the illusory free-will would not, I think, dispute your notions in defining freewill as you do, but they would question whether there is any genuine freedom within it, and if there is no freedom within it, how can it be freewill as anything other than illusion?
Free-will only seems to be threatened if we assume that the proximate determination occurring inside the person's head is in turn entirely determined by more spatio-temporally remote states of the universe and by the inexorable laws of physics. The free-will-is-an-illusion assumption has historically been that everything that happens in the universe, including all of a person's purposes and motivations inside their heads, has always been predetermined by the preexisting states of the universe and by the laws of physics.
Not necessarily pre-determined (which is why I don't like the use of "determined by" to merely mean "the result of"). If one considers the universe to operate with an element of randomness, or is indeterministic, but that randomness/indeterminism is still allowed by the universal laws, then there is no predetermination yet freewill would be, per their argument, still illusory.
Since I'm arguing for compatibilism, I want them to agree with me. (Why in the world would I want them to disagree?) But why is it merely an appearance? Why is the word 'decision' in full quotes?

It is in quotes because to consider it a genuine decision is to beg the question. It is the very issue that is being questioned.
So how do we define "making a decision"? I would say that most people would see the term as being the output from freewill. If we consider freewill to be genuine, then a decision is the output from freewill. However, if a decision is merely the output of, say, a deterministic process, akin to a computer filtering data and reaching a conclusion (as per IBM's Watson), then we can be considered to "make a decision" if that process occurs within our heads/brains.
As such the term "decision" does not say anything about freewill being illusory or otherwise.
So I put it in quotes to ensure that people do not make the assumption that the term implies a genuine freewill.
Unless the person, whose decision process it is, wanted to do something different instead. In which case the causal process would have gone in a different direction, would have involved different internal goals, purposes and motivations, and people would probably be insisting that different path is the only way that things could have unfolded.
It's necessary that whatever happens is what happens. But that doesn't mean that whatever happens necessarily had to happen. To reach that conclusion, we would need to add an additional deterministic assumption.
Sure. I'm not a strict determinist. But even with randomness within the operations at the minutest level, it is the inability to do anything other than that which happened that is crucial.
If I roll an indeterministic die, for example, the output can be any number from 1 to 6, but I can not "choose" which it is. But the output is not predetermined.
That sounds like a statement of metaphysical faith to me. But that's neither here nor there, since I don't think that anything important rides on it.
I don't think it is faith. I'm not saying that nothing can ever defy them, but if that happens then those laws will be debunked and new ones will be developed. But they are laws precisely because nothing
yet has ever defied them.
But moving on...
Ok, let's agree to that for the sake of argument. I generally agree with it myself, even if it is an item of metaphysical faith in my case.
Let's call it an assumption, then.
Ok, let's agree with that one too. I fully expect that whatever neuroscience eventually discovers in the 'black box' of the brain/mind, it will be entirely physicalistic.
Ok. We're on a roll...
So if we agree that the rest of the universe along with the laws of physics aren't determining what human behavior must be, then what do you think is determining what it eventually is? If it's a person's own on-board decision process that's steering their behavior, however naturalistic and causal that process might be, I don't see why I should conclude that free will is just an illusion. The person is still behaving in accordance with his/her own goals, desires, purposes and motivations. He/she isn't being coerced.
First, I'm saying that it is not
just the external environment. Clearly it has some impact - often quite significant.
As for the rest, this is what I would consider to be merely a matter of definition of freewill... i.e. your definition is that the process occurs within the human, irrespective of what that process is, and much of the process is feedback loops of other processes within the human... etc.
For me, there is still no freedom within the process. And if there is no freedom, how can I say that there is any freewill? There is certainly the conscious appearance of it (the consciousness being another process etc), but is there any actual freedom to do anything?
So this is where we seem to differ, I think.
Maybe part of the difficulty here is that I (and perhaps CC as well) were addressing philosophy's long-standing free-will/determinism problem.
Possibly.
And maybe some here are really arguing about a different question, about the existence or non-existence of supernatural souls. Perhaps 'free-will' is being collapsed together and identified with belief in the existence of souls. Which suggests that if somebody can successfully make an argument that what happens inside people's heads is entirely natural, entirely in keeping with and ultimately explainable by the principles of natural science, so that there aren't any ghostly supernatural influences reaching in and moving things around, then free-will must therefore be an illusion. Or something.
I'm trying to keep it away from that, and would not argue beyond request for evidence of it, which would get tiring.
It kind of looks that way to me, the way that people talk about causation somehow contradicting free-will (it arguably might, if people equate 'cause' with 'determine') while stoutly insisting that determinism has nothing to do with it.
"Determine" has specific connotations - as in if the universe was rewound and played over, the same things would result. The argument that I (and I think Baldeee, and Cluelusshusband etc) make is that it is merely the lack of freedom to select the output that is important... and there is no freedom in an indeterministic environment that follows the universal laws. At most there is randomness (and thus indeterminism). So whether the universe is strictly deterministic (I don't think it is) or not, really does not matter. And the closest thing such as Clueluss and others have to succinctly word that is to merely talk about causation. But causation does not imply determinism.
If one merely uses "determine" to mean "is the result of..." without invoking the determinist philosophy, then okay, but it can get confusing.
For the record, I don't believe in the existence of supernatural souls either. I hypothesize that our decision processes will turn out to be entirely physicalistic. But I do think that our free-will intuitions are a lot more than illusions, precisely because I think that they can successfully dodge the determinism difficulty. Souls have nothing to do with it.
For the record, I don't believe in supernatural souls either. And I think the rest depends on what you consider freewill to be. And for me it needs to have genuine freedom to be considered a genuine freewill.