Enjoyed your reply, thanks. Got me thinking. Wanted to get this bit out the way first, but it turned out long, seriously looong, so will have to reply to the bulk of your post later.
Yeah sorry, I'll address that directly, hopefully it makes sense when I explain what I mean (even if we disagree about the implications).And why are you still repeating this idea that behaviour doesn't require mental decisions or willing? It does. Without intentionality models of behaviour do not function. I wrote a fair amount on that in my last post and I'm not sure you've addressed that?.
There are patterns of physical interactions so reliable and predictable we call them laws - Physics (biology and chemistry being reducible to physics). Now the Higgs Bosun's been confirmed we have what physicists believe is the basic structure of a standard model of physics, what the world is made of and how it works, why what happens, happens. (Hmmm is this Physics an assumption? It might not be the whole story, but I'd say it's well enough evidenced to be a reliable working assumption at the levels of granularity it adresses). So, us being middling sized critters our behaviour is in principle explainable by looking at the position of our physical parts, applying the laws which apply to middling sized systems, and if we know all the required physical info, our behaviour is predictable. That's the claim physics implies, summed up with La Place's Demon, or physical determinism.
We see this physics in action in our own unconscious behaviour, our knee-jerk reflexes, our systemic autonomic regulation of our breathing, heatbeat, digestion, blinking, etc, even when we're asleep. No mental causal input is necessary for those behaviours, just physical cause and effect. We might even have the mental experience of dreaming we're running, or grabbing a juicy orange, but if the necessary physical causal neuronal connections aren't activated, our bodies just stay lying in bed. The majority of the brain's functioning doesn't involve mental experience, it physically 'decides' and executes when to take a breath, pulsate heart muscles and so on. So we can say physical causation looks like a necessary condition for all physical behaviours in conscious systems like us, and a necessary and sufficient condition for at least some of them. [You can skip the rest if you're happy with that]
So the evidence suggests Physics alone can do at least some behavioural jobs for us, where-as mental causation alone can't (I can't will the orange to come to me because it's missing the necessary physical causal links), but can physics do them all? When we believe we're making mental decisions and willing our actions (eg I'm hungry and decide I'm going to eat an orange, and my hand grabs the orange), is anything different happening outside of the same physical cause and effect which makes my knee jerk and my heart beat?
An important point to remember is that if neural correlation is correct, the physical causes and effects must be happening during both autonomic behaviours like breathing, and mentally deciding I fancy eating the orange and grabbing it. If that's not correct, it's hard to understand how we'd function 'outside of' physics. (So I suppose I'm making an assumption that our brain and body physical causal connections must be sufficiently complex to carry out all its behaviours, to have them physically happen - but once I've assumed neural correlation is true, then this follows).
We can imagine how it works in my rough n ready description to Felix above - photons bouncing off an orange, hitting my eyeball, causing physical effects throughout my optical systems, causing physical effects in my various neural systems (where the 'decision' is physically made) causing physical effects in my arm's motor systems - and I've grabbed the orange. Imagining it working in much more complex scenarios involving symbolic representations like words, or situations like complex social interaction is much harder, but the physical stuff still has to be doing the work of getting the motor systems to physically move, and presumably neural correlation still holds. We must be sufficiently complex physical systems for the trillions of potential physical causal patterns of neuronal connections to physically spark the neurons involved in the decision, and to physically execute the behaviour. Even if that behaviour is typing symbolic letters on a screen, or the neural correlates of adding 2 + 2 'in our heads'. The neural correlates have to be able to physically do the work, however complex or symbolic - or we somehow defy the laws of physics. If you then throw in mental causation on top of the physical processes which can already fully account for all our behaviour, it looks unnecessary, duplicating something which would happen anyway, 'overdetermines' the behaviour.
That's what I mean when I say mental causal input is apparently unnecessary in principle (we don't have the technology to look at trillions of connecting neuronal patterns in detail to confirm it), and why people think mental experience might be epiphenomenal baggage with no causal role (like the steam off the railway engine, an ineffectual by-product of certain physical interactions). The physical engine, the neurons, are all in place following the laws of physics, to be all that's necessary and sufficient to account for all our behaviour. So the argument goes that in principle mental causation (mental deciding and willing) looks unnecessary. Decisions are made via neural connections resulting from external or bodily physical stimuli, and we just imagine we're deciding things mentally. And there are experiments (admittedly limited by our crude technology) which suggest that at least some mental decisions are predictable, by scanning brains and knowing what simple decision someone will make (eg when they decide to press a button) before they've consciously decided. See Libet et al.
So there's the in principle argument, backed up by tentative experimental findings, that our mental decisions might be post hoc explanations of our behaviour which has already been decided and executed via physical cause and effect alone. Free will, mental causation, is a story we tell ourselves to help make sense of our mental model of the world and ourselves. You might say it's the nuts n bolts of the determinism position, the reality of what it means in conscious beings. This is the one side of the conundrum I mentioned before, not the end of the discussion, but I believe it clearly needs addressing re whether free will exists. A conundrum which ideas like monism and dualism try to address... in my framing.
(Excuse any scientific inaccuracies, hopefully the gist is correct and makes the point).