Since I missed last week (bad way to start the New Year, no?), I thought I would give you a few "big", interrelated heresies this week: Monarchianism, Adoptionism (or Dynamic Monarchianism--similar, but slightly distinct) and Sabellianism (more commonly known as Modalism).
Monarchianism is a 2nd century heresy that emphasizes God as one person—the Father (antitrinitarian). It originally rose as an attempt to combat Tritheism by overemphasizing (to the point of diminishing and eliminating two persons of the Trinity) the singularity of God. There are two contradictory models of Monarchianism: Adoptionism (or Dynamic Monarchianism) and Sabellianism (or Modalism). Psilanthropism (and, by extension, Unitarianism) is considered an Adoptionism heresy, and Noeticism and Patripassianism are considered Sabellianism heresies (although Noeticism came first, historically).
Adoptionism is a 2nd century heresy of the Arianism family. It purports that Jesus was ‘adopted’ as the Son of God at either His baptism, His resurrection or His ascension (depending on which sect to whom you were speaking) because of His godly human life up until that point. Some historians have traced it all the way back to the time of Christ on earth. It was one of two main forms of Monarchianism (the other being Sabellianism, also known as Modalism). Adoptionism is also known as “Dynamic Monarchianism”, and denies the eternal pre-existence of Christ. Adoptionism was condemned as heretical by a decree from Pope Victor (who was Pope from 190-198). Samosatenism was a 3rd century adoptionist heresy that taught Jesus was a man who ‘kept’ himself sinless and ultimately achieved union with God (while considered closer to Adoptionism, it appears to not fit well with either branch of Monarchianism), after which it seemed to ‘die’ out. It reemerged in the 8th century in Spain (Spanish Adoptionism), teaching then that Christ was the Son of God with respect to His divine nature, but Jesus, as a man, was merely the adopted Son of God; and again from the 12th century on as “Neo-Adoptionism”. Psilanthropism was the 18th century Unitarianism take on Adoptionism.
Dynamic Monarchianism: see Adoptionism. This is a Monarchianism and Arianism heresy. The main distinction between Adoptionism and Dynamic Monarchianism (usually used interchangeably) is that they deny the Logos, or person of Christ, and teach that the Holy Ghost is simply a force of or the presence of the Father. They teach that Jesus was only a man. Unitarianism, known then as Psilanthropism, picked up on this heresy in the 19th century, still practicing it today, along with Christadelphianism and Jehovah’s Witnesses.
Sabellianism (also known as Modalism) is an antitrinitarian Monarchianism (the other branch being Adoptionism, or Dynamic Monarchianism) heresy that teaches the Father, Son and Holy Ghost are simply different modes or aspects of One God, perceived by the believer, rather than three distinct persons in one Godhead. They do not deny the divinity or humanity of Jesus (and while they believe in a singular God, the “mode” of the Son was imbued in Jesus), like believers of Arianism or Monophysitism. There is no way for God to be all three modes simultaneously; He may only be one at a time. The United Pentecostal and United Apostolic Churches still teach Modalism today, saying that the mode of God is “Jesus only” now and that baptism is required for salvation (no unbaptized person will ever be “saved”). On the other hand, believers in Unitarianism teach that God simply is one person, with no distinct “modes”.
As mentioned in the descriptions, it is important to understand these heresies because they are still being practices in several "church" bodies. So next time a Jehovah's Witness comes to your door or you run into a Unitarian, you have a conversation starter!