a better question would be, what constitutes free will? if everything we do, say, and think has a cause, or a combination of causes, or a process that motors our actions, then what is the definition of determinism? do we have free will if some of our “causations” are internal vs. external? conscious vs. unconscious?
some of our actions/decisions are automatic, some are conscious. exclude the automatic actions (like breathing, reflexes).
what determines a conscious action? genetics and the way we were raised (nature and nurture) are the biggest ones, although there are others like prenatal conditions, diet, substance abuse… all external and beyond our control. or things like personality, temperament, passion, interest… which are internal and cannot be pinned down as to what, exactly, causes our personality to develop. or our temperament. what causes some people to be more passionate than others, and some to have more interest in various things than others? we certainly can control our reactions to things, to a great extent. we can swallow our pride, or control our anger, divert our lust, cultivate an interest or deliberately ignore one. we can overcome phobias, become more outgoing, cheer ourselves up, etc… so we do have free will if the definition is based on control. these are all examples of controlling an external reaction, but there are examples of people controlling physical reactions.
a person in emotional turmoil will often have physical symptoms, such as a gut-wrenching fear, or headaches/bellyaches/jointaches caused by depression. a person can alter his or her perception based on emotional fears or the *desire* to experience something physical… an example of the former being hypochondriacs, an example of the latter being hysterical pregnancies. so not only does the physical world stick its fingers in the mental world, but the mental world often sticks its fingers in the physical. people have often been able to exert their will in intense physical ways, like enduring the elements or lifting heavy objects to save loved ones, but whether that will is “free” or not depends on how you define “free will.”

I’d like to response that this is precisely the issue: what is determined by circumstances (determinism), and what do we have ‘control’ over, and what is that – to have control over something, and is free will only a conscious thing, or something that perhaps the unconscious has something to do with as well?

Defining these things may seem to help, but I don’t think that it really does. Anyhow, it’s beyond me to define them.