Largely due to the efforts of Augustine of Hippo, the Western church condemned Pelagius and his heresy, Pelagianism, at the Second Council of Orange in AD 529. The same council also condemned a weaker form of the Pelagian heresy that has come to be known as semi-Pelagianism.
Traditionally, most scholars have said that semi-Pelagianism originated in the writings of the French monk John Cassian, who lived at roughly the same time as Augustine and Pelagius, during the late fourth and early fifth centuries AD. Essentially, semi-Pelagianism tries to steer a middle ground between Pelagius and Augustine. While rejecting the Augustinian view of unconditional election to salvation, semi-Pelagianism nevertheless affirms the necessity of grace for salvation. The problem is that semi-Pelagian thought denies the radical depravity into which sin has plunged the human race. In semi-Pelagianism, grace is necessary but human beings take the first step toward God. Without the assistance of grace, fallen men and women retain the ability to seek the Lord of their own accord. They need grace to be saved, but God’s grace does not take the initiative in salvation. It is available to all if they will just seek it out. This is different from Augustinian and biblical theology, which says that grace is selective and that the initiative is always the Lord’s. He makes the first move in salvation. No sinner can seek God of their own accord, and the only people who seek Him are those whom He first sovereignly and effectually draws by His saving grace (see John 6:44).
At root, the real disagreement between semi-Pelagianism and Augustinianism has to do with whether God’s saving grace in regeneration is synergistic or monergistic. Semi-Pelagians say divine grace is fundamentally synergistic—God and human beings work together to bring about regeneration. Men and women seek God and then God responds with His grace. Augustinians, including Reformed thinkers such as John Calvin, affirm that divine grace is monergistic in regeneration. The Lord is the only one who works to bring about the new birth, and His grace finally saves all those to whom it is given. His grace is not given to everyone but only to the elect and then not be-cause of anything in the elect themselves. To put it another way, biblical, Augustinian thought is insistent that we love God only because He first loved us (1 John 4:19) and that God guarantees His elect will love Him, overcoming their resistance to His love.
Augustinianism and semi-Pelagianism ultimately disagree regarding the power of God’s love and beauty. Is God’s love so effectual and is He so lovely that those to whom He reveals His salvation cannot finally reject Him, or are His love and beauty of a lesser character that cannot convince everyone whom He wants to save? By upholding Augustinian thought, we are powerfully declaring the glorious love and beauty of our Creator.