I strongly agree on the statement, that the problem is undecidable. The axiom is that the machine that predicts the future exists, so then we can use that as a lever. Build another machine that predicts predictor (antipredictor). Then you can prove it by observing antipredictor. If antipredictor lights up, you dont press the button (because you want to fool predictor) but then the future in which you pressed predictor does not exists (because antipredictor lighting up automatically means you must have pressed it!). Essentially, creating new devices that predict the future might as well create different systems from which you wont be able to observe other systems. In fact the whole dispute is pointless, even if our lives are deterministic, you wont be able to see it. In our world we can only use heuristics to determine the future of systems, but complete simulation of the future is impossible, because we would need to account for everything (and use this everything to compute everything). You can only build such machines / deduct such observations when you are outside of the system.

We can deduct another experiment. Take 2D world in which 2D creatures live. For them 3D space is space-time. For us it's 4D. Then 4D creatures can deduct that our world is deterministic or not. But 4D creatures cannot determine if their space-time is deterministic. 5D creatures can say that. It goes to infinity, if at least one space-time is non-deterministic then whole system is non-deterministic. The fact that this experiment can go into the infinity makes subject undecidable.

I think it's decidable, as long as we agree on our definitions and assumptions.

So for example let's assume that free will is the ability of an agent to do otherwise. I don't think that view of free will is compatible with agents being non-random consistent beings. For a decision to be mine it must be determined by my memories, preferences, personality, skills, experiences, etc. The decision must be determined by my state, or the decision does not come from me. But if the decision comes from my state, then given my current state I could not do otherwise.

To me that's just a trivial statement that I am a consistent being with characteristics that persist over time, and that I am responsible for my deliberate, considered actions. If I, this person and my current state, do not determine my actions in a straightforward cause and effect way, how can I be responsible for them? So I certainly hope my actions are determined.

> I think it's decidable, as long as we agree on our definitions and assumptions.

I guess, you mean if I accept your definitions, assumptions, and their underlying premises which will most likely lead us to conclude that your point of view is more reasonable, don’t you? :)

That is, yes, once we agreed on every underlying concept scopes and the rules to play with them, chances are far better that we agree on the conclusions. But the first part is actually a big part of what is so difficult with communication, isn’t it?

Oh absolutely, that's exactly my point. Even my example definition has ambiguities.

I defined an agent as being a non-random consistent being, but what does consistent mean exactly? What I meant was that I have reasons for my actions. After all, if I can give reasons for my actions, and I'm not deluded, surely my reasons determine my actions? Take that deterministic relationship away in the name of some abstruse philosophical concept of 'free will' being the ability to do otherwise, and why did I perform that action exactly?

Of course dualists have a very different conception of a human actor. They deny that we are 'mere' mechanisms and that there must be more to humans and their minds than the merely physical. Whatever that 'more' is. How exactly that gets round the problem I really don't know. Ive never read a convincing account of that. You're right, we need to dig into these assumptions. What is an actor? What is a consistent being? In dualism, what is this dual other thing, that isn't physical and what role does it play in decisions? That is the real question for dualism. Free will or lack of it is merely a consequence.

That's a way to see it. Here is another:

We are complicated pieces of biochemical machines. Atoms, molecules, cells interacting with each other. No magic, nothing special. Just nice, repeating patterns in infinity.