Formal principle and material principle are two categories in Christian theology to identify and distinguish the authoritative source of theology (formal principle) from the theology itself, especially the central doctrine of that theology (material principle), of a religion, religious movement, tradition, body, denomination, or organization. A formal principle tends to be texts or revered leaders of the religion, while a material principle, its central teaching. These categories were articulated, developed, and utilized by the Lutheran scholar, F.E. Mayer, in his The Religious Bodies of America in order to facilitate a comparative study of the faith and practice of Christian denominations in the United States. This is also treated in a theological pamphlet entitled, Gospel and Scripture by the Commission on Theology and Church Relations of the Lutheran Church—Missouri Synod.

F.E. Mayer's findings

Eastern Orthodoxy

• • Formal Principle -- the Bible and the "sacred tradition."
  • Material Principle -- Jesus Christ's work of theopoiesis or theosis (θέωσις), the ultimate deification of man. They cite Athanasius of Alexandria from his Incarnation of the Word: "Christ assumed humanity that we might become God."