Modalistic Monarchianism

Modalistic Monarchianism, also known as Modalism or Oneness Christology, is a Christian theology upholding the unipersonal oneness of God while also affirming the divinity of Jesus. As a form of Monarchianism, it stands in contrast to Adoptionism (Dynamic Monarchianism), a Christology of the divine nature of Jesus that views Jesus as not pre-existent as a distinct divine person, although empowered by God the Father through the Holy Spirit. Dynamic Monarchianism is closely associated with Adoptionism, a theology of the Godhead that argues that Jesus became God's son at a moment in time when God adopted or exalted him into divinity. The term modalism was first used by Trinitarian scholar Adolf von Harnack, referencing this belief.

Modalistic Monarchianism is opposed to Trinitarianism and binitarianism. Followers of Modalistic Monarchianism consider themselves to be monotheistic in a strict sense—similar to Jews and Muslims—and they argue for no plurality of persons in the theology of God. They consider God's person to be absolutely one and assert that the person of God reveals himself to creation through different "modes" (or "manifestations")—namely, the Father, Son, and the Holy Ghost—without limiting his modes or manifestations.

In this view, the godhead is understood to have dwelt in Jesus from the incarnation as a manifestation of the God of the Old Testament (Hebrew Bible). The terms "Father" and "Son" are then used to describe the distinction between the transcendence of God and the incarnation. To frame it another way, "Father" and "Son" are technical terms that distinguish between the deity of God alone (i.e., the Father) and the deity of God joined to the human nature in Jesus (i.e., the Son). Lastly, since God is a spirit, it is held that the Holy Spirit should not be understood as a distinct person but rather as the one God, acting in the world.

Modalistic Monarchianism is closely related to Sabellianism and Patripassianism, two ancient theologies condemned as heresy in the Great Church and successive state church of the Roman Empire.