Free Will is best understood as a complex idea combining two antagonistic concepts - freedom and determination - in a temporal sequence.
First comes the consideration of alternative possibilities, which are generated unpredictably by acausal events (simply noise in neural network communications). This free creation of possible thoughts and actions allow one to feel "
I can do otherwise."
Next comes
de-liberation and determination by the will, the unfreeing of possibilities into actuality, the decision that directs the tongue or body to speak or act.
After the deliberation of the will, the true sentence "
I can do otherwise" can be changed to the past tense and remain true as a "hard fact" in the "fixed past," and written "
I could have done otherwise."
Thus we have the
temporal sequence which
William James saw so clearly a century ago, with chance in a
present time of random alternatives, leading to a choice which grants consent to one possibility and transforms an equivocal future into an inalterable and
simple past.
Free undetermined alternatives are followed by
willed, determined choices. As
John Locke knew more than three hundred years ago, "free" is an adjective that describes not the will, but the human mind.
Chapter 6.6 - Language 
