Pelagianism derives its name from Pelagius who lived in the 5th century A.D. and was a teacher in Rome, though he was British by birth. It is a heresy dealing with the nature of man. Pelagius, whose family name was Morgan, taught that people had the ability to fulfill the commands of
God by exercising the freedom of human will apart from the
grace of God. In other words, a person's free will is totally capable of choosing God and/or to do good or bad without the aid of Divine intervention. Pelagianism teaches that man's nature is basically good. Thus it denies original sin, the
doctrine that we have inherited a sinful nature from Adam.
http://carm.org/pelagianism