*The following is drawn from Richard Muller’s Post-Reformation Reformed Dogmatics, Volume 1 along with my own paraphrase and reflections.
What is a First Principle?
In theology, a first principle (principium) is a starting point/beginning/arche/source/ground/axiom that is the cause of all doctrines in the Christian religion.
First principles are a priori, self-authenticating, and cannot be deduced from any other proposition or assumption. They are necessarily and immutably true, self-evident, and indemonstrable.
According to Aristotle, “It is common to all principles to be the first thing from which a thing either is, comes to be, or is known. And of these some are intrinsic and others extrinsic” (Aristot., Met. 1013a.15–19).
The first principles of any given discipline (theology, arithmetic, geometry, physics, etc.) must be identified as 1) a principle of being (principium essendi) or essential foundation, and 2) a principle of knowing (principium cognoscendi) or cognitive foundation.
The principle of being is essential for the existence of theology.
The principle of knowing is essential for the knowledge of theology.
God As The Principle of Being (Principium Essendi)
God is true, self-evident, necessary, and knowable. His existence is more foundational and more basic than demonstration, “for in Him we live, and move, and have our being” (Acts 17:28). It is God’s existence that makes the discipline of theology possible.
Scripture As The Principle of Knowing (Principium Cognoscendi)
Holy Scripture is the divinely given, authoritative, and infallible cognitive foundation for theology. God’s knowledge of Himself (archetypal theology) is what makes human knowledge of God (ectypal theology) possible.
Archetypal Theology is the higher science that supplies the principles used as the basis of conclusions in the subalternate science of Ectypal Theology. All true theology reflects the divine archetype and that archetype cannot be known in and of itself but only through gracious self-revelation. Reason, therefore, cannot be the cognitive foundation of theology inasmuch as it is not a divine self-revelation but only an instrument for understanding revelation. Since, moreover, the archetype infinitely transcends nature and since the ultimate end of theology is of grace and not of nature, the natural order and its revelation cannot be the cognitive foundation of Christian theology. What remains is the divine self-revelation in and through the Word as recorded in the biblical witness. Thus, the Word of God written is the principium cognoscendi theologiae.