Term used to describe a belief in early church history that Father, Son, and Spirit are not eternal distinctions within God's nature but simply modes (methods or manifestations) of God's activity. In other words, God is one individual being, and various terms used to describe Him (such as Father, Son, and Holy Spirit) are designations applied to different forms of His action or different relationships He has to man. See Chapter 10 - ONENESS BELIEVERS IN CHURCH HISTORY for further historical discussion. Also called modalistic monarchianism, Patripassianism, and Sabellianism. Basically, modalism is the same as the modern doctrine of Oneness.
A Trinitarian heresy, which treats the three persons of the Trinity as different "modes" of the Godhead. A typical modalist approach is to regard God as active as Father in creation, as Son in redemption, and as Spirit in sanctification.