Let the course of events, including events in my brain (or yours or his or its) be deterministic. It seems to many people that there is no place for free will. Even our thoughts are determined.
However, if we examine closely how a human brain (or chess program) deterministically makes decisions, free will (or imitation free will if your philosophy forbids calling it real free will) must come back in. Some deterministic processes consider alternative actions and their consequences and choose the actions they think have the most preferred consequences. This deterministic decision process uses a nondeterministic theory to present the set of available actions and the consequences of each of them.
When a person, animal, or machine reacts directly to a situation rather than comparing the consequences of alternative actions, free will is not involved. So far as I can see, no animals consider the consequences of alternative actions; hence they don't have free will. Others think that apes sometimes do compare consequences. A relevant experiment is suggested in section 7. Using free will is too slow in many situations, and training and practice often have the purpose of replacing comparison of consequences by automatic reaction to a situation.
We believe this simple theory covers the most basic phenomenon of human free will. We'll call it simple deterministic free will and abbreviate it SDFW. Robots with human-level intelligence will also require at least this much free will in order to be useful.
Beyond having free will, some systems are conscious of having free will and communicate about it. If asked to tell what it is doing, humans or some machine will tell about their choices for action and say that they intend to determine which action leads to the best consequence. Such a report, whether given externally or contemplated internally, constitutes the human sensation and the human report of free will. SDFW does not require consciousness of having free will or the ability to communicate about it. That's what's simple about SDFW. Thinking about one's free will requires theoretical structure beyond or above SDFW. So will considering actions as praiseworthy or blameworthy. SDFW also doesn't treat game theoretic situations in which probabilistic mixed strategies are appropriate.
In AI research one must treat simple cases of phenomena, e.g. intentional behavior, because full generality is beyond the state of the art. Many philosophers are inclined to only consider the general phenomenon, but this limits what can be accomplished. I recommend to them the AI approach of doing the simplest cases first.