Three Fundamental Principles of Theology

We thus identify three fundamental principles for theology: God is the essential foundation (principium essendi); Scripture is the external cognitive foundation (principium cognoscendi externum); and the Holy Spirit is the internal principle of knowing (principium cognoscendi internum). The foundations of theology are thus trinitarian: The Father, through the Son as Logos, imparts himself to his creatures in the Spirit.

Source: Herman Bavinck, John Bolt, and John Vriend, Reformed Dogmatics: Prolegomena, vol. 1 (Grand Rapids, MI: Baker Academic, 2003), 207.