Would a Roman Catholic theologian ever side with Luther against Erasmus on whether the will is free or not? Yes.
The book pictured to the left is Catholic Scholars Dialogue With Luther (Chicago: Loyola University Press, 1970). Yes, it's my copy. The book is an anthology of chapters from Roman Catholic theologians on aspects of Luther. One chapter is entitled Erasmus versus Luther- Compounding the Reformation Tragedy by Harry J. McSorley, C.S.P. Around the time of the writing of this chapter, Father McSorely had written an entire critique of Luther's battle with Erasmus: Luther Right or Wrong? An Ecumenical Theological Study of Luther's Major Work, The Bondage of the Will.
While Father McSorley doesn't agree with all of Luther's argumentation in the Bondage of the Will, he does stand with Luther in condemning the position argued by Erasmus. Remember, it was the Papacy that prodded Erasmus to engage Luther and write De libero arbitrio.
I found many of McSorley's comments honestly revealing. The following are but a small sample:
First, Erasmus shows little appreciation of the genuine meaning of Luther's thesis of the unfree will, namely, that the will of fallen man apart from grace is totally incapable of doing anything for salvation, totally unfree to do anything that is good in God's sight. Instead of coming to grips with this biblical concept of man's slavery to sin, Erasmus concentrates his attention on the secondary, non-biblical supporting argument which Luther used in the Assertio--the argument from the absolute necessity of all events (p.111).
Secondly, and more unfortunately, we find the leading scholar of the Roman Church doing a bad job in presenting the Church's teaching on free will. Erasmus defines free will as "the power of the human will by which man can apply himself toward or turn himself away from the things which lead to eternal salvation." This is a seriously defective definition of free will. Instead of defining free will in terms of the ability to choose between certain alternatives, Erasmus defines free will in terms of salvation--without mentioning grace. Erasmus gives no hint in his definition that man the sinner is enslaved to sin until he is liberated by grace. The definition is surely one of the "extraordinary blunders" which, according to P. Hughes, characterize De libero arbitrio (p.112).
A third striking fact about De libero arbitrio is Erasmus' unawareness that the Church, centuries before, had taken an official stand against a modified version of Pelagianism that came to be known, late in the sixteenth century, as Semipelagianism. Erasmus was not alone in his unawareness of the Second Council of Orange (529 A.D.) and its confirmation by Pope Boniface II in 531. As H. Bouillard has pointed out, the decrees of Orange II were in some way lost during the middle ages and are cited by no authors from the tenth until the mid-sixteenth centuries. This did not mean that the doctrine of Orange II was lost. Such biblically oriented theologians as Bernard, Anselm, Thomas Aquinas, and Gregory of Rimini, who recognized Augustine as their theological master, especially in the doctrine of grace, were all agreed that the sinner is a slave to sin unless he is liberated by the prevenient grace of Christ. Thomas, without knowing of the decrees of Orange II, was even able to say that it is a "truth of faith" that the very beginning of faith is in us from God (p.112).
Now, several years after his excommunication, Luther finds the leading Catholic intellectual saying that the following Neo-Semipelagian position is a tenable option: ". . . [H]aving not yet received the grace which forgives sin, man can, by his natural powers, perform works which, as they say are morally good, by which justifying grace is merited not de condigno but de congruo..." (p.113).
Erasmus reveals his total unawareness of the Church's rejection of Semipelagianism in the Hyperaspistes, his lengthy response to Luther's reply to him in De servo arbitrio. Of the Ockham-Biel opinion, Erasmus says that as far as he knows it has not been rejected by the Church (p. 113).
Further, developing the concept of "natural" or "common" grace that he had mentioned in De libero arbitrio, Erasmus distinguishes a "human faith, " which is "a type of knowledge preparatory to the light of faith, "from a "faith which through grace justifies." Then he explains: ". . as there are degrees of justice, so there are degrees of gifts until you reach that which is merely natural. But even this is grace, since God is the author of nature. Thus Augustine is needlessly afraid of saying that the initium gratiae arises from man." Erasmus seems completely unaware that Pelagius had said exactly the same thing to Augustine: free will is a donum Dei; therefore no other donum is necessary! In this sense Pelagius could also say as Erasmus does: "We ascribe everything to God's goodness" (p. 113-114).
We have not compared Erasmus' opinion to the teachings of Orange II and Trent in order to indict Erasmus as a heretic. His unawareness that the Church had once taken a definitive stand in favor of the doctrine of fallen man's bondage to sin exculpates him from the charge of formal error or heresy. That the decrees of the Second Council of Orange went astray and that a new form of the old Semipelagian error arose among late medieval theologians would seem to be more than anything else the result of negligence in the exercise of the Church's teaching office (p.114).
As for Erasmus, it is sufficient to point out that his views on grace and free will are not normative for Roman Catholics. The Catholic commitment to the grace of God is recorded above all in Scripture and in the Councils of Orange II, Trent, Vatican I and Vatican II.Secondly, in De servo arbitrio Luther presents the most powerful biblical argument for fallen man's bondage to sin that the Church had heard since St. Augustine. Such a reformation proclamation was truly needed in the first quarter of the sixteenth century. It is no exaggeration to say that until the Council of Trent reaffirmed what was taught by the Second Council of Orange, Martin Luther was one of the few theologians in Germany who unhesitatingly defended the biblical and Catholic teaching on man's bondage to sin. He proclaimed that fallen man could do nothing whatever without grace to prepare himself for salvation. This he did at a time in which many, many Catholics - -including Erasmus--had either lost this truth or were uncertain about it" (p.117).