Medieval Italian poet Dante Alighieri, exiled for life from his native Florence, took the opportunity to write a magnificent trilogy — the Divine Comedy — in which he tours Hell, Purgatory, and Heaven. The Comedy is more than a poetic masterpiece. It is a profound philosophical and theological reflection on this life and on eternity. Remarkably, although Dante’s immediate guides through the unseen worlds are, famously, the Roman poet Virgil (70 BC–19 BC) and later, a childhood sweetheart Beatrice (who died young), his philosophical guide is the philosopher and theologian Thomas Aquinas.

The metaphysics, the ethics, and the theology of the Divine Comedy deeply reflect Thomas’s influence. That is remarkable, considering that Dante (1265–1321 AD), who was only a child when Thomas died in 1274, was writing the poem in the very early 14^th century when Thomas’s work was still quite controversial. Some of it was banned by the Church.

Nonetheless, Dante took the risk of structuring his Comedy, the greatest poem of the European Middle Ages, in accordance with his thinking. One might say that Dante’s poem is a poetic expression of Thomas’s philosophy and theology. And the issues he dove into the same ones we face today. One of them is, do we have free will? And why does it matter?

Dante offers deep insight into the meaning of free will in the second book of the three, the Purgatorio. His Purgatory is a place where redeemable people get a chance to face up to and delete the things that hold them back from eternal life in Paradise.

Dante is there with his guide Virgil because Beatrice, in an attempt to rescue him from utter despair, has prevailed on Heaven to let him see how people’s choices shape their destinies. He has already toured the Inferno with Virgil and he hopes to meet Beatrice again if he makes it through Purgatory.

Although Dante structures much of his poem using an astrological framework of the movement of the heavenly bodies, he does so for political reasons. He does not believe that the alignment of the planets determines our wills or fates. Following Thomas and the Christian tradition generally, he defends the reality of free will and the falsity of physical determinism. He makes a subtle and rather beautiful argument in favor of free will that still makes sense today.

Dante points to a conflict between astrology and free will. Astrology is very like modern materialism. Many ancient thinkers believed that the human will was controlled by planets and many modern thinkers believe that it is controlled by molecules. The difference is that astrology is cosmological determinism, whereas materialism is molecular determinism. So in the old system, our fate is determined by the orbits of planets and in the new one by the orbits of molecules. The question Dante addresses is: if determinism is true and free will is not real, can you be ethical?

In Purgatorio XVIII 43-45 and 58-60, Virgil, who is Dante’s guide through Purgatory, observes

for if love [i.e. the will] is offered from outside us
and if the soul moves on no other foot [i.e. if determinism is true],
it has no merit in going straight or crooked…
These are innate in you just like the zeal in bees
for making honey, and this primal inclination
admits no positing of praise or blame.

Dante points out that if the will is wholly determined by outside factors — astrological or molecular — then there’s no merit or fault in what we choose to do. If we have no free will, we are mindless — and just as lacking in praise or blame — as insects.

He explains that without free will there is no such thing as ethics (64-69):

this is the principal in which is found
the measure of your merit, as it welcomes
and then winnows good from guilty loves [i.e. good will from bad will]. 
Those who in their reasoning reached the root [i.e. classical and Christian philosophers]
recognized this innate freedom
and thus bequeathed their ethics to the world.

On Dante’s view, the basis for ethics is freedom of the will. Without free will — that is, if our will is controlled by the planets or by our molecules and not by us — we have no basis for ethics at all. We are insects striving by our instincts with no merit or blame in doing right or wrong. Without free will, there is no right or wrong. There is merely activity with no ethical significance.

Dante concludes: (70-75)

Let us posit as a given: every love that’s kindled in you
arises of necessity [i.e. as temptations]. 
Still the power to restrain it lies with you.
That noble power is called free will by Beatrice,
and so make sure that you remember this
if she should ever speak to you.

Dante cannot think of anything better than that Beatrice should speak to him again so he presses on.

If there is no free will, we are as much a slave to our instincts and our temptations as insects are. We cannot even speak rationally of ethics if we deny free will. For materialists to be consistent, they would need to abjure all ethical systems. A materialist who denies free will on the basis of determinism denies himself any recourse to ethics at all.

Materialism is a logical mistake, and not really a coherent system of belief.

Mind Matters News offers a number of articles on free will by neurosurgeon Michael Egnor including

Can physics prove there is no free will? No, but it can make physicists incoherent when they write about free will. It’s hilarious. Sabine Hossenfelder misses the irony that she insists that people “change their minds” by accepting her assertion that they… can’t change their minds.

Does “alien hand syndrome” show that we don’t really have free will? One woman’s left hand seemed to have a mind of its own. Did it? Alien hand syndrome doesn’t mean that free will is not real. In fact, it clarifies exactly what free will is and what it isn’t.

But is determinism true? Does science show that we fated to want whatever we want? Modern science—both theoretical and experimental—strongly supports the reality of free will.
How can mere products of nature have free will? Materialists don’t like the outcome of their philosophy but twisting logic won’t change it.

Does brain stimulation research challenge free will? If we can be forced to want something, is the will still free?
Is free will a dangerous myth? The denial of free will is a much more dangerous myth.

Also: Do quasars provide evidence for free will? Possibly. They certainly rule out experimenter interference.

and

Can free will even be an illusion? Michael Egnor reiterates the freeing implications of quantum indeterminacy

Also, by Baylor University’s Robert J. Marks: Quantum randomness gives nature free will Whether or not quantum randomness explains how our brains work, it may help us create unbreakable encryption codes