Principia Theologiae
...the Protestant scholastics declare two principia theologiae, a principle or foundation of knowing (principium cognoscendi) and a principle or foundation of being (principium essendi). The former is Scripture, the self-revelation of God, and the latter is God himself, the self-existent ground of all finite existence
Richard A. Muller, Post-Reformation Reformed Dogmatics: The Rise and Development of Reformed Orthodoxy; Volume 1: Prolegomena to Theology, 2nd ed. (Grand Rapids, MI: Baker Academic, 2003), 126-127.