Pelagianism
Pelagianism is a belief that original sin did not taint human nature (which, being created from God, was divine), and that the will is still all powerful. Thus, Adam's sin was merely to set a bad example for his progeny, but did not cast mankind from grace. It also reduces the significance of Jesus Christ to merely "setting a good example" for the rest of us. In short, man has full control, and thus full responsibility, for his own salvation.
The view was popularized by a monk and theologian, Pelagius, who was a favorite in Rome and later was forced to flee to Africa. Pelagius was contemporary with Augistine of Hippo who fought against this view, leading to its condemnation as a heresy by pope Zosimus (in the Tractoria, the Eastern Council, and emporer Honorius in 418.