St. Thomas never gave a free will theodicy. Freedom is absence of compulsion, and absence of compulsion in the will does not explain how evil is even possible, much less how it could happen in fact. as far as STA was concerned, given that most of the universe was composed of the blessed angels and the saints, most of the universe was composed of beings that experienced no compulsion in their wills and yet could never commit a moral offence.
Evil has to be explained by imperfection: concretely, it happens because we can know things that we do not think about; more generally it happens because of a unique state of men in history and in via. God makes beings that can know things they don’t think about by making intellects with potency – and this was usually explained by his desire to create a universe with every grade of perfection. The broader historical predicament – unknowable except by revelation – was because of desire to glorify both man and himself in the Incarnation.
Just Thomism 
Wade McKenzie said,
June 4, 2014 at 2:33 pm
“… most of the universe was composed of beings that experienced no compulsion in their wills and yet could never commit a moral offence.”
And a question is: Why wasn’t it possible to create man this way in the beginning?
James Chastek said,
June 4, 2014 at 2:51 pm
The “could never” can be taken in two ways: either as involving no antecedent act of free, rectified will, or as involving one. In the first way, only God is incapable of committing an offence to pervert the will. In the second way, a creature can be good if it has an immaterial existence, like an angel or a disembodied soul.
God cannot create a being who did not have to choose to be good in order to actually be good. One piece of evidence is that we know we can’t be good in that way. We would have to have upright wills simply in virtue of existing, but we know this makes no sense. Our wills can’t be good by logical necessity, and so require some antecedent action.
vetdoctor said,
June 6, 2014 at 7:22 pm
If I were to ask all my questions you would ban me so I will contain myself to one. Could you explain a little this remark, ” Evil has to be explained by imperfection: concretely, it happens because we can know things that we do not think about . . .” ?
Thank you, I enjoy your posts and even understand some of them.
James Chastek said,
June 7, 2014 at 9:31 am
Moral evil involves doing something that you know is wrong and evil. But “evil” is opposed to good, and so evil is the undesirable. But how can one desire the undesirable? There is a contradiction here, and so it seems we cannot commit a moral evil.
The conclusion is absurd and so we have to explain the problem. Aristotle gives two answers to this, but both involve saying that we commit evil when we know something is evil but are not thinking about the fact that it is evil; either because we are considering something else about the object we are tending to, or because we don’t make it a principle of our action.
Fr Aidan Kimel said,
June 20, 2014 at 9:04 pm
Is anyone here acquainted with Herbert McCabe’s critique of the free-will defense of evil, as presented in his books*God Matters* and *Faith Within Reason*? In addition to arguing that free will is perfectly consonant with divine predestination–divine causality does not compete with free human choices–he also maintains that God could have created a world in which every human being was perfectly free and yet no one sinned.