Thomas Aquinas has had a long but, on the whole, not very happy history among Protestants. While some early Protestant reformers were well versed in Thomistic theology, Martin Luther was not among them.

Most of Luther’s important teachers were disciples of the Franciscan theologian William Ockham. The Occamists taught a theology of grace that tilted in a decidedly Pelagian direction. Pelagianism is theological shorthand for a theology that deemphasizes the role played by grace in human salvation and overemphasizes the role played by human free will. Gabriel Biel, the Occamist theologian Luther knew best, even argued in a burst of anthropological optimism that human beings were able to love God perfectly without the assistance of grace. While Biel admitted that the human intellect and will were fallen, he thought they were nevertheless largely undamaged by sin. He concluded therefore that acts of extraordinary moral heroism, unassisted by grace, merited divine favor. Not surprisingly, Luther found no authorization in St. Paul or St. Augustine for such a rosy view of human nature, and he rejected all Occamist accounts of salvation.

A prominent early-20th-century Roman Catholic historian, Joseph Lortz, agreed with Luther that Biel’s theology of grace was thoroughly “uncatholic” and he thought Luther was quite right to protest against it. The problem, from Lortz’s perspective, was that Luther seemed unaware of the best Catholic antidote to the Pelagianizing tendencies of Biel—the thought of Thomas Aquinas.

If only Luther had been trained in Thomistic theology, argued Lortz, he would have had at his disposal all the resources he needed to oppose Biel and to do so without drifting into what Catholics regard as heresy. Had Luther studied Aquinas at Cologne rather than the Occamists at Erfurt and Wittenberg, he would have found a better way through his theological crisis and would have avoided the tragedy of the Reformation.

Lortz’s thesis was immensely influential but not altogether satisfying. The principal difficulty was that it presupposed a state of affairs that did not exist—namely, that only one Thomas Aquinas was on offer in the 16th century. Actually, there were at least three.

The Dominican theologian John Capreolus (d. 1445) portrayed Aquinas as a thoroughly Augustinian theologian. Whenever readers encountered ambiguous passages in Aquinas that might be interpreted in a less than fully Augustinian way, Capreolus advised them to remember this simple rule: always choose the reading closest to the spirit of St. Augustine. That would uncover the mind of St. Thomas.

Thomas de Vio Cardinal Cajetan (d. 1534)—also a Dominican—was not so sure. He was far more impressed by Aquinas the Aristotelian philosopher. In Cajetan’s view, Aquinas, more than any other scholastic thinker, had successfully adapted the vocabulary and categories of Aristotle for Christian use. This was not an easy task, and Cajetan could only admire what Aquinas had achieved. Whereas Capreolus read Thomas as a faithful disciple of Augustine, Cajetan read him as the foremost Christian interpreter of Aristotle.

Biel (d. 1495) offered a third version of Aquinas, this one in complete agreement with the Pelagianizing tendencies of the school of Ockham. When Luther read Biel’s account of Thomas’s theology, he encountered a theologian whose doctrine of sin and grace differed in no significant way from the Occamist teaching Luther had come to despise.

In short, Lortz misread the situation. The problem was not what Luther did not know, but what he did know. Far from offering Luther resources to combat the Occamist account of sin and grace, the Aquinas that Luther knew reinforced it.

Nor would Luther have been helped by paying closer attention to the Aristotelian Aquinas offered by Cajetan. Luther thought that Christian theology could be renewed only by breaking free from Aristotle. The problem with Aristotle from Luther’s perspective was not that he believed in the eternity of the world and the mortality of the human soul (which he did), but that his philosophical vocabulary was ill-suited for theological use. Grace cannot be understood as habits and acts, and the Aristotelian notion that the repetition of good acts makes anyone who performs them righteous turns St. Paul’s theology on its head.

In Luther’s view, theology deals with God in his relationship of judgment and grace toward sinners, and deals with sinners in their relationship of faith and faithlessness toward God. Therefore the proper vocabulary of grace is relational rather than metaphysical. One does not become a theologian with Aristotle, cried Luther, but only without him.

In his early lectures on the Psalms, Luther insisted that the word substance in the Bible refers not to the quiddity or whatness of a thing but to what “stands under and supports it.” The substance of a human being, therefore, is defined by the foundation on which he or she rests. Who human beings are is determined by what they trust, by what—when push comes to shove—they are willing to risk their lives on.

In other words, the vocabulary of the philosophers obscures, willy-nilly, the intention of the Bible, which defines human beings not by their quiddities and qualities but by their faith and hope. No philosophical description of human beings, resting as it does on what can be seen and measured, can reach the profundity of biblical anthropology, which rests upon invisible relationships.

The most important thing about a human being for Luther is what that human being trusts, loves and expects. Human beings are defined by things that cannot be seen, things that in the nature of the case can only be hoped for. When Luther asked, “What, then, is a human being?” he answered that a human being is not a rational soul individuated by a body, as Aquinas might have put it, but a creature who trusts either the true God or an idol. On this question Aristotle can offer no useful insights.

While Protestant thought before Kant found its own uses for the philosophy of Aristotle, Protestant thinkers remained haunted by the ghost of Luther. Aquinas was for them either a Pelagianizing theologian who relied too little on grace and left too much to human free will or a philosophical theologian who counted too heavily on human reason and too little on divine revelation. Biel and Cajetan had succeeded in driving Capreolus’s account of Aquinas from the Protestant imagination.

Aquinas was not helped by his increasing prestige among Catholic theologians outside the Dominican order—including, of course, the Jesuits. Since Protestants characteristically thought that Catholic theology was insufficiently Augustinian, they were not surprised that Catholic theologians admired a theologian who embodied this deficiency. There were even some Protestant theologians who thought that Aquinas had constructed an immense philosophical substructure based on reason alone, to which he had added a flimsy theological superstructure grounded in divine revelation.

Other developments made matters worse. Kant put an end to metaphysical speculations for many Protestants, while Friedrich Schleiermacher developed a new kind of liberal dogmatics that took Kant’s critique fully into account. Liberal Protestants in the 19th century were quick to reject all things Greek (that is, metaphysical) and embrace all things Hebraic (that is, ethical).

The heart of the Christian gospel for many liberals from Albrecht Ritschl to Adolf Harnack was an ethical message. Jesus was a preacher of the kingdom of God in which a new ethic was to be followed, a fact some thought had been obscured by Nicaea and Chalcedon. The ancient councils had lost in their metaphysical categories the liberal Protestant vision of a “young and fearless prophet of ancient Galilee, whose life is still a summons to serve humanity.” Not surprisingly, there was no room for Aquinas in this particular theological inn.

The correction to liberal theology made by the dialectical theology of the early 20th century scarcely improved Protestant approaches to Aquinas. Karl Barth, Rudolf Bultmann, Friedrich Gogarten and Emil Brunner turned to the teaching of the Protestant reformers of the 16th century for inspiration, and while these so-called neo-orthodox theologians did not simply repristinate the theology of Luther and Calvin, they saw no reason to abandon the prejudices of the reformers against scholastic theology.

Barth was particularly hostile to Aquinas’s appeal to natural theology. He argued that Calvin had rejected natural theology (which was true) and concluded that he had rejected all natural knowledge of God (which was false). Similarly, he argued that Aquinas had affirmed a role for natural theology (which was true) but had overestimated its role in theology (which was false). Aquinas made it clear from the very beginning of the Summa Theologiae how limited was the scope he assigned to natural theology.

As Aquinas understood matters, natural theology could be pursued successfully only by trained people who had both the intellectual power and the leisure to extract from nature, by reason alone, what the natural order has to tell about nature’s God. Even then, whatever they could learn would be fragmentary and inevitably mixed with error. Furthermore, reason could not wrest from nature the mysteries of the Trinity or the two natures of Christ. Indeed, without the self-revelation of God, reason alone could never discover what it most needed to know: namely, how God redeems wayward and erring humanity.

There were intimations by the middle of the 20th century that the old Protestant stereotypes of Aquinas might be crumbling around the edges. Per Erik Persson in 1957 published Sacra Doctrina: Reason and Revelation in Aquinas. The book was notable in treating Aquinas as a theologian rather than a religious philosopher and in offering a sympathetic account of Aquinas’s views not only on reason and revelation, but on a broader range of theological issues central to his thought. Persson pushed aside Biel and Cajetan and engaged Aquinas directly.

Since then, other Protestant thinkers have joined Persson in his direct engagement with the source. Christian ethicists like Stanley Hauerwas have utilized what Aquinas wrote about the cardinal and theological virtues in their own work on the formation of Christian character. Other theologians, newly liberated from the Kantian prejudices of the Enlightenment, have found Aquinas’s subtle and nuanced account on metaphysical questions bracing.

Even the biblical work of Aquinas on Romans and Job has elicited the interest of Protestant historians, who have found his commentaries to be sources of wisdom and insight into the biblical drama of redemption. In short, Aquinas the Augustinian theologian has emerged from behind the older Protestant stereotypes. Protestants have rediscovered the Aquinas Luther never knew—the Aquinas of John Capreolus.

It would be too much to assume that Aquinas will ever be as central a theologian for Protestants as he has been for Catholics. But Protestants have begun to put an end to their own self-imposed impoverishment. They have opened the ranks of the theologians with whom they are in regular conversation to include Aquinas. It is a development long overdue.

See also Timothy Renick's review of the same books and Jason Byassee's discussion of recent Protestant literature on Aquinas.