Formal principle and material principle are two categories in Christian theology to identify and distinguish the authoritative source of theology from the theology itself, especially the central doctrine of that theology, 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 is its central teaching. Paul Tillich believed the identification and application of this pair of categories in theological thinking to have originated in the 19th century. As early as 1845 the Protestant theologian and historian Philip Schaff discussed them in his The Principle of Protestantism. They were 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, the ultimate deification of man. They cite Athanasius of Alexandria from his Incarnation of the Word: "Christ assumed humanity that we might become God."
Material Principle – "Man's soul, since it comes directly from God, is good and strives for reunion with God, realized in the beatific vision of God. Man's body is subject to sin and is alienated from God. Therefore man must be progressively justified, i.e., be made just. This result is effected when through the sacraments man enters into the 'state of grace' and observes the commandments which the church... by her 'divine commission,' imposes upon the 'faithful.'"
Lutheranism
Formal Principle – the Bible alone
Material Principle – "a synopsis and summary of the Christian truth" that people are justified by God's grace through faith in Christ alone.
Anglicanism
Formal Principle in general—The Bible, the authority of the church, and reason. Specifically, for individuals of different churchmanship:
