Monarchianism, sometimes called Monarchism, is a heretical theological movement that arose within the second and third century Church. It consists of a set of beliefs that emphasize God as being one, that God is the single and only ruler.
This emphasis conflicted with the doctrine of the Trinity, of God as Father, Son, and Holy Spirit. Models of resolving the tension between the two principles in favour of God's oneness were proposed in the 2nd century but rejected as heretical by the Church.
Monarchianism in and of itself is not a complete theory of the relation of the Father, Son, and Holy Spirit, but a simple tenet that requires further extension. There are basically two contradicting models of Monarchianism:
- Modalism considers God to be one person appearing and working in the different "modes" of the Father, the Son, and the Holy Spirit. The chief proponent of Modalism was Sabellius, hence the view is also called Sabellianism. It has also been labeled Patripassianism by its opponents because it purports that God the Father suffered on the cross.
- Adoptionism holds that God is one being, above all else and wholly indivisible and of one nature, it reconciles the "problem" of the Trinity (or at least Jesus) by holding that the Son was not co-eternal with the Father, and that Jesus essentially was granted deity-hood (adopted) for the plans of God and his own perfect life and works. Different flavors of Adoptionism hold that Jesus was "adopted" either at the time of his baptism, or ascension. An early exponent of this belief was Theodotus of Byzantium.