Yes - the conscious will of the human soul
How many times do you need it pointing out that this
isn't an answer?
Even if we assume, for the sake of argument, that human souls exist, they still have to arrive at their choices
somehow. There must be a
decision making process going on in your magical, non-physical realm.
It is the nature of that process that is the point - you can't just pretend it doesn't exist or is not subject to logic. People (souls, if you want) make choices for
reasons - which is where determinism (or some degree of randomness) comes in.