The confessional manuals that followed Aquinas were consumed by a controversy for over a century. Probabilism, the position that a confessor may follow any solidly probable opinion about what the law requires even when a stricter opinion is also probable, became standard practice among many Jesuit moral theologians by the seventeenth century, intended to avoid binding penitents to the harshest available reading of a doubtful case.
Jansenist writers attacked the practice as moral laxism dressed up in scholastic language, most famously in Blaise Pascal's Provincial Letters of 1656 and 1657, which mocked probabilist casuistry as a system for excusing almost anything a confessor wished to excuse. Rome eventually intervened against the excesses on both sides: a series of condemnations targeted lax propositions associated with probabilism, while Jansenism's own rigorist alternative, which tended toward withholding absolution and communion until a penitent's contrition was judged sufficiently severe, was condemned as well.
Alphonsus Liguori, an eighteenth century Neapolitan bishop, proposed the resolution that eventually won out, equiprobabilism, holding that a penitent may follow a probable opinion favoring liberty only when it is at least as solidly grounded as the opinion favoring the law, a narrower door than unrestricted probabilism and a wider one than Jansenist rigorism. He was later declared a Doctor of the Church and patron of confessors and moral theologians, and his cautious middle path, not either extreme, became the working standard of Catholic moral theology in the centuries before the Vatican II reform.