Does freedom entail responsibility, punishment, and reward? What is the role of compulsion, will, and choice in human action? St. Thomas Aquinas vigorously defended the reality of free will, not simply because he felt that it was divinely revealed—“He himself made man from the beginning, and left him in the hand of his counsel” (Sirach 15:14)—but that it also had consequences for ethical life, the social order, and epistemology.
Aquinas dealt with evil in many of his writings, but the question of free will, evil, and ethics reveals his position most visibly in his Disputations on the Question of Evil. The respondent is questioning the reality of free will under God’s totality (in many ways, prefiguring and anticipation Calvinist theology which grew out of scholastic theological debate). In responding to the assertion that humans have no free will and that God is the prime mover of everything, including human action, Aquinas responds by citing the authority of Holy Writ (Sirach 15:14) before launching into a deeper critique as to why the allowance and compulsive theological vision is heretical and problematic.
For not all compulsion is violent, only external compulsion: the movements of nature are compelled but not violent, since violence—origination outside—is incompatible with both the natural and the willed—both of which originate inside. The suggestion, however, is heretical since it destroys the notion of human action as deserving or underserving (cf. Rom. 2:6, 2 Cor. 5:10, 1 Pt. 1:17): somebody so compelled to act that he can’t avoid it doesn’t seem to be doing anything deserving or undeserving. The opinion is also philosophically anarchic, not only opposed to the faith but destroying the foundation of ethics. For if we are not in any way free to will but compelled, everything that makes up ethics vanishes.
Aquinas takes for granted that this type of mechanistic-puppet anthropology is “opposed to the faith” and so launches into a critique of this compulsion theology and anthropology by underscoring the problem that it would pose to ethics. Ethics is founded on the notion of good and bad, obviously. That there is a moral law and that rational creatures since “free will is a power of reason” and that the essence of man as the imago Dei is to know the Good and True and abide by, and in, it, further entails that to miss the mark is sin and to hit the mark is sanctification. So bound up in ethics is the theological concept of sin, which is manifested due to ignorance of the True and Good and the deprivation of the True and Good in actualized movement (since humans are potentiality moving toward actualization).
The anthropology behind the compelled actus of man denies the reality of the imago Dei first and foremost. To have been made in the image of God is to have been made in the image of Truth, Wisdom, and Love—to be made in truth, wisdom, and love, for truth, wisdom, and love. God is also a free acting agent, as all know in Christian theology. This too is imparted into the order of the cosmos and to human beings as the instantiated embodiments of the image of God who is also free. Hence freedom is passed to human beings because humans are made in the image of freedom.
To be free means to be left to counsel, to be left to thought and contemplation. It also means to be left responsible for the choices one makes. Compulsion theological-anthropology strips all of this away. It depreciates the imago Dei to being an empty puppet, it denies the imputation of sin to man, makes God the Author of sin, and is inconsistent as to who is responsible for sin. This is the supralapsarian dilemma in Calvinism. If God is the Author of our will, and our will sins, then God is the Author of sin. If God is the Author of sin why are humans held responsible for something that they did not do in free choice?
As Aquinas says, not only is this strand of theological thought heretical, he also has the foresight in seeing the disastrous consequences to social and ethical life. God wills for humans to do the Good. But the “human will can diverge from God’s will.” In denying free will and arguing that all things are compelled either by the direct energies of God or God’s allowance of lower activities to come about, then the reality of sin is also destroyed. To chalk everything up to compulsion is to transfer sin from the human will falling short of God, Truth, and the Good, to God Himself or the mechanistic laws of causality.
What is the purpose of law and order? What is the existence of instruction and education for? Why be considered with virtue? All of these questions should naturally follow from the compulsion theory. To argue that these constructions exist for self-interest, is one then not conceding an implicit moral reality if self-interest and self-gain is bad?
Free will makes man accountable for his actions, both to the state and the eternal law of God. Free will also comes with tremendous responsibility and the potentiality of man. As Aquinas goes on to explain, the reality of free will allows man to progress in knowledge, grow in spiritual and ethical maturity and virtue, and be transformed and divinized in becoming more like God (knowing and acting in accord with Truth, Wisdom, and Love), “Love is said to transform lover into beloved because it moves a lover towards the actual thing loved, while knowledge assimilates by bringing a likeness of what is known to the knower.” But the inverse must also be true by the logic of entailment. For true freedom to exist there must also be the falling short and the consequences thereof. A consequence-free life is no freedom at all. For there to be no consequences means there were no alternative choices available—all seemingly different options and choices are illusory and are one and the same. This falling short is due to lack of knowing which results in a deficiency in love—the desire to love and be loved is turned into the desire to lust and be lusted upon.
Law exists because law manifests the reality of goodness and badness in instantiated life. The law exists to inform you of the good and exists to punish wrongdoing. Order exists to guide one to the good, which entails the possibility of a non-good (evil) because if there was no good to be ordered to in the first place there would be no need for order to begin with. The same is true for instruction and education. If there is no knowledge then there is nothing to act to, toward, or realize in life. The very existence of instruction and education entails a good to know, it therefore implicitly acknowledges Truth to understand and instantiate in life. This is what virtue is about: knowledge of the Good and True and living by that standard of Truth.
The denial of free will erodes all of the above. The denial of free will devolves man into compelled beast in the field and denies his rationality. The denial of free will leads to a consequence free, nihilistic, and hedonistic life, because it is easy. A life without freedom is an easy life. One never need take responsibility for any action. It is also the manifestation of the ignorant life, “[p]eople are led to embrace [this denial of free will]…partly by sophistical reasoning to which they can’t find the answers.” Since finding the answers is difficult, people resort to the easy solution by saying there is no answer which allows the anarchic free-for-all. And if you don’t like the outcome of this relativistic and “compelled” life, well, that implicitly implies that there is another way, that there is a Good and True standard to come to know and conform by, and that human potential desires.
Aquinas’ defense of free will is also a defense of humanism; that is, the uniqueness of humans as images of God with rationality capable of knowing the Good and True. The defense of free will is also a defense of the reality of sin and the possibility for ethical life and moral order in the world. Without free will, moral freedom is threatened.
In the end, Aquinas anticipates certain radical theologies and ethical movements that derived from those theologies. The denial of free will destroys the reality of sin. The denial of free will also destroys the reality of ethics. (Ethics is the non-theologized reality of the theology of sin.) The denial of free will also destroys the reality of law, order, education, and virtue. Without freedom we truly do live in a nihilistic cosmos where nothing matters and everything is left to self-compulsion to consume and satiate the appetites.
 It is obvious to anyone knowledgeable in Christian history that the Biblical canon included the Deuterocanonical texts. From the Church Fathers to medieval commentaries and ecclesiastical documents, you see repetitive citations and appeals to the authority of Scripture using Deuterocanonical works. St. Augustine even devoted an entire chapter in The City of God arguing for the primacy of the Septuagint over the “Hebrew” Bible (15.13, 18.42-43).
 Cf. Summa Theologiae, 1a.79.2-3.