Free will as nonlinear transformational effectiveness
A man can do what he wants, but not want what he wants.
— Arthur Schopenhauer
Free will does not and cannot imply without cause, randomness or unpredictability. All those qualities, although present in complex systems, would contradict the notion of willful intent. What we want, and therefore do, must be based on reasonable ground. Random convulsions are not our understanding of volition. It is defined as purposive striving and thus has to have a purpose, it has to be based on cause.
Thus, does free will exist? If so, what is free will? Can there be a reasonable definition? I think so.
Of course, looking for free will as seen from a strong philosophical viewpoint is a futile effort. It's asking for rainbows end. Reality, reason and logic, forbid libertarian free will. For one there is the impossibility of choice. Though you may, to a limited extent, outweigh the problem of choice by accepting the many-worlds is an interpretation of quantum mechanics. More important, and I think crucial, for the fallaciousness of metaphysical free will is the fact that it is impossible due to Gödel's incompleteness theorems. No system can understand itself for that the very understanding would evade itself forever. A bin trying to contain itself. This prohibits sufficient control over internal causes, which I think, are ultimately indistinguishable from causal relationships between a defined system and the environment.
There's no scientific reason to believe that we have free will. There's no buffer zone that we've found in any of the physical laws of how the universe works to make room for free will. There's non-determinism; but there's not choice. Choice is the introduction of something, dare I say it, supernatural: some influence that isn't part of the physical interaction, which allows some clusters of matter and energy to decide how they'll collapse a probabilistic waveform into a particular reality.
— Mark Chu-Carroll
Scientists think that there are phenomena that qualify to be defined as 'free will'. Specifically endogenous processes generating behavioral variability and thus non-linearity. But I think this is not enough.
Free will is a middleman. Consciousness between cause and effect. The intelligent refinement of causation into an effective agent. The sun at your back - your shadow in front. You are the shadow player. Nevertheless, to claim sovereignty is trying to get ahead of your own shadow. You imprint reality with a pattern of volition. But not without its implicit consent.
A system qualifies as free if you can show that the specific effectiveness and the complexity of transformation by which a system shapes the outside environment, in which it is embedded, does trump the environmental influence on the defined system.
In other words, mind over matter. You are able to shape reality more effectively and goal-oriented and thus, in a way, overcome its crude influence it exerts on you.
What does this mean? For example, children and some mentally handicapped people are not responsible in the same way as healthy adults. They cannot give consent or enter into legally binding contracts. One of the reasons for this is that they lack control, are easily influenced by others. Healthy humans exert a higher control than children and handicapped people. You experience, or possess a greater extent of freedom proportional to the amount of influence and effectiveness of control you exert over the environment versus the environment over you.
Though this definition of free will only work once you arbitrarily define a system to be an entity within an environment, contrary to being the environment. The universe really just exists. And it appears to us that it is unfolding because we are part of it. We appear to each other to be free and intelligent because we believe that we are not part of it.
Nevertheless, I think it might after all be a useful definition when it comes to science, psychology and law. It might also very well address our public understanding of being free agents.
How much sense does all this make? I don't know. I admit that I do not have the expertise to base my ideas on firm ground or even judge the credibility of these thoughts. Nonetheless, so far the above is as close as I can get towards a satisfying framework for the notion of free will.