In order to answer this question in full it will be required to respond to the three aspects of free will mentioned;
1-When and 2-how did free will originate?
3-How to explain ontological free will?
The concept of free will arose as a psychologically driven fear that if the universe is completely deterministic in every aspect of existence, then humans are merely automatons, doomed to a pre-determined life. This is not a very appealing option.
A further complication of this sorry state would be that no ethics or morals would be possible, since determinism would render culpability for evil inapplicable.
All of this originate in the 17th century when the existence of an anthropomorphic God, who personally oversees and intervenes in human lives, became to be dispelled. This gave rise to a new and greater fear; that if there is no God, to direct and protect what becomes of all the 'bad' players and 'evil' in the world.
In line with resolving this dilemma Descartes 'discovers' that the human mind can operate freely because we have a pituitary gland which can 'twitch' its way to providing humans with free choice
Descartes asserted that the mind through its own power can exert control over its own decision-making process:
*"Descartes’s notions concerning freedom of the will, can lead one to wonder how his belief in a mechanical universe is compatible with his notions of an immaterial mind, a totally free God, and one’s innate ability to express their freedom. To Descartes, an immaterial mind is possible due to his belief that God is a force which precedes the laws of the universe, and by freely causing these laws, it is unlimited in all ways. By being unlimited, God has the power to create, and one can infer that to Descartes, something such as miracles are possible due to God’s ability to intervene in nature, because God’s existence is outside of nature’s domain."
Furthermore, Descartes believes one’s ability to express their freedom derives from them being independent substances that are reflections of God’s essence, and because God’s essence is free, it follows that people are naturally free as well.
Yet, the consequences of holding to these beliefs, I believe, can lead one to misunderstand their ability to be free. This is because, his notions can give way to questions, such as: How can a free, and immaterial mind be united to a body whose movements are determined? How could God be uncompelled in all ways, if all beings are subject to the laws of nature? And finally, how can it be the case that people are free, even when Descartes openly states people are not only physically compelled by the laws of nature, but they are also limited mentally?*
Author, Rocco A. Astore graduated in 2019 with a Masters degree in Philosophy from New School For Social Research in New York, NY.
Spinoza and Descartes lived in that 17th century mentioned earlier, although Descartes died before Spinoza's birth. Coincidentally, Spinoza produced a book on Descartes philosophy, the "Cogita Metaphysica", which came to be recognized as the clearest explication of Descartes philosophy.
Now a complication arises because Spinoza did not much admire Descartes work. In fact he believed him to be hypocritical in claiming that he could 'control' his thoughts in such a way as to 'doubt' all that he knew.
Of course, that raise the question of why Spinoza maintained this disparaging view? and thus we come to attempting to explain both 'free will' and 'determinism' all in one fell swoop. So here it comes.
Spinoza explicitly uses the phrase "free necessity": "I say that a thing is free, which exists and acts solely by the necessity of its own nature. Thus also God understands Himself and all things freely, because it follows solely from the necessity of His nature, that He should understand all things." (This is not a personal god, no theism here!)
Spinoza defines “free” and “necessary” (or “constrained”) in this manner:
“That thing is called free, which exists solely by the necessity of its own nature, and of which the action is determined by itself alone. On the other hand, that thing is necessary, or rather constrained, which is determined by something external to itself to a fixed and definite method of existence or action” (Ethica, Definition VII.)
God, (or Nature, which is the same thing) is free in the sense that of being self-caused and self-determining.
One further clarification on Spinoza's use of 'determined'(not determination). For Spinoza a contingent being (human) is 'determined to act in a particular manner', which is no more than saying that a human will , walk on the earth, will breathe air and will need to take on nourishment to survive.
In no way did he intend this to be misconstrued as humans every thought and action is predetermined.
Finally, why does this belief in 'free will' continue to dominate the philosophical airways and to play such a pivotal role in ethics and morals. Strangely enough it all comes down to the confusion that arise in formal logic's concept of the excluded middle. People tend to assume that this assertion of a proposition being either true or false extends to their own lives. They believe in what can be termed the 'either/or' fallacy.
That is that 'I as a human am either completely determined OR completely free'. This leads to all manner of confusion. But that is not part of this question, so adieu!