late 2nd c. – 272

Monarchianism: dynamic and modalist (Noetus, Sabellius, Paul of Samosata)

Some theologians defended the unity of God against the Gnostic aeons and Marcion's two gods; Tertullian called the path they took "Monarchianism." It is divided into dynamic (Theodotus the Tanner, excommunicated by Victor of Rome, later Theodotus the Banker and Artemon) and modalist, or Patripassianism (Noetus of Smyrna, Praxeas, and in the East Sabellianism). In the West, Hippolytus and Tertullian opposed Modalism.

The most prominent representative of dynamic Monarchianism was Paul of Samosata, bishop of Antioch. A synod in 268 condemned him, but under the protection of Queen Zenobia of Palmyra he kept his see until 272, when Emperor Aurelian expelled him.

A related episode was the dispute between the two Dionysii – of Alexandria and of Rome – over the interpretation of Proverbs 8:22. In it the bishop of Alexandria, fighting Sabellianism, made the first notable use of the term "homoousios" (of one essence).