This absolute monergism could thus also be called “mono-causalism.” It is contrary not only to Augustine and the whole Catholic tradition, but also to the Westminster Confession, which teaches that the eternal decree of God by which he does “ordain whatsoever comes to pass” works in such a way that “neither is God the author of sin … nor is the liberty or contingency of second causes taken away, but rather established” (3.1; cf. also 5.2). The point of this teaching, which is couched in the language of Thomas Aquinas and agrees with his doctrine, is that God’s working in all things does not mean that creatures have no power to work, but rather that the creatures’ power, will and work derive from the work of God, and precisely for that reason are real, just like all God’s works. God’s primary causality therefore does not undermine or replace the secondary causality of creatures, including their free will. God has ambassadors, apostles and other servants with a will of their own and work to do, even while he is always indispensably at work in them. The two forms of causality are not incompatible or in competition with one another.
Mainstream Calvinism is thus at one with Catholicism in rejecting absolute monergism. The place to locate the difference between Catholicism and Calvinism concerning monergism is rather in the fact that the whole Roman Catholic tradition since Augustine is synergist about salvation. For Catholicism our works of love (made possible by operative grace in the beginning and aided by co-operative grace throughout) are necessary for salvation. That’s precisely the purport of Trent’s denial of the sola fide: faith alone is not enough for salvation without works of love (Decree on Justification, articles 10-11).
However, there is a division within Catholicism on the point about monergism with respect to faith. Whereas one important strand of Catholic theology, including Aquinas and the Dominican tradition, promotes an Augustinian monergism about faith, another strand, most powerfully represented by the 16th-century Jesuit Luis de Molina, defends a form of synergism about faith. Molinism is thus something like the Catholic form of Arminianism. In the De Auxiliis controversy around 1600, the Pope adjudicated between these two positions, decreeing that both were legitimate and neither side could accuse the other of heresy. This was of course not a relativist move: the two positions are probably irreconcilable, and if so then at least one of them is in error in some way. But the pope’s decree meant that such error is not heresy and does no harm to the faith, so the debate may continue but must do so in mutually respectful terms.
There is of course no one on earth to adjudicate between Catholics and Protestants. But perhaps it will help to be aware, at least, of the difference between absolute monergism and the more modest monergism about faith, justification and salvation which is the legacy of Luther and Calvin.
This is precisely the level of discourse that should guide our discussions.