At the head of the Semi-Pelagian party stood John Cassian, the founder and abbot of the monastery at Massilia, a man of thorough cultivation, rich experience, and unquestioned orthodoxy… . [Cassian’s most important works] are his fourteen Collationes Patrum, conversations which Cassian and his friend Germanus had had with the most experienced ascetics in Egypt, during a seven years’ sojourn there.
In this work, especially in the thirteenth Colloquy, he rejects decidedly the errors of Pelagius, and affirms the universal sinfulness of men, the introduction of it by the fall of Adam, and the necessity, of divine grace to every individual act. But, with evident reference to Augustine, though without naming him, he combats the doctrines of election and of the irresistible and particular operation of grace, which were in conflict with the church tradition, especially, with the Oriental theology, and with his own earnest ascetic legalism.
In opposition to both [Pelagianism and Augustinianism] he taught that the divine image and human freedom were not annihilated, but only weakened, by the fall; in other words, that man is sick, but not dead, that he cannot indeed help himself, but that he can desire the help of a physician, and either accept or refuse it when offered, and that he must cooperate with the grace of God in his salvation. The question, which of the two factors has the initiative, he answers, altogether empirically, to this effect: that sometimes, and indeed usually, the human will, as in the cases of the Prodigal Son, Zacchaeus, the Penitent Thief, and Cornelius, determines itself to conversion; sometimes grace anticipates it, and, as with Matthew and Paul, draws the resisting will—yet, even in this case, without constraint—to God.