Kant talked about heteronomy, the condition of an individual's being at least partly under the control of influences other than his or her own reason, and therefore not truly exercising free will. Of course this early Enlightenment ideal strikes us as a bit naive today, and obviously we recognize that we are animals with a physical form.
But there's no need to put such extreme, stark requirements on free will for its exercise to be unclear. A perfect example is my own appetite for chocolate. At the moment, I have avoided all forms of chocolate for 16 days. As far as I can remember in my life, this is a record. In the past when I wasn't so lucky I would declare "no chocolate for one month", and then three days later at 7-11 I would break down and get a Hershey bar.
Now, clearly in those 3-day cases I was unable to follow my prior edict, but at that moment, chocolate is what I wanted. And I acted on the urge. How is this not free will? Because the urge came from a pre-conscious animal drive for sugar and fat, and/or conditioning from previous purchases at that same 7-11? If ultimately what we call reason, and our entire executive center, is a slave of the passions as Hume suggested and as seems to be the case, how could it matter whether I was acting directly on an animal urge or on some long-term plan that was dictated by animal urges?