SabellianismIn Christianity, Sabellianism (also known as modalism) is the second century belief that the three persons of the Trinity are merely different modes or aspects of God, rather than three distinct persons. It is attributed to Sabellius, who taught a form of this doctrine in Rome in the second century. Hippolytus knew Sabellius personally and mentions him in the Philosophumena. He knows Sabellius disliked Trinitarian theology, but he calls Modal Monarchism the heresy of Noetos, not that of Sabellius. Hippolytus thought he had very nearly recounciled Sabellius to the mainstream church. However, during the controversy surrounding Paul of Samosata, the Patriarch of Antioch who was deposed in 268 for his Christology, Sabellius' name was mentioned. No one in Antioch had heard of him, but his name was associated with Rome. So they wrote to Rome about him. Pope Dionysius replied in a letter of which only a small fragment has been preserved, but this letter was enough to make Sabellius famous among the Greek theologians.
Another name for this doctrine is Patripassianism from the Latin words patris for "father", and passus for "to suffer". This name was given because the doctrine implies that God the Father came to earth and suffered in the form of God the Son.
Historic Sabellianism taught that God the Father was the only person of the Godhead, but the Oneness doctrine of today says that this one member of the Godhead is Jesus. Oneness doctrine claims that when Scripture describes the Father or the Holy-Spirit, it is actually Jesus, who is only revealing Himself as one of the other modes of God. Some Oneness followers call this the "Jesus Only doctrine".