Philosophy takes its rise from common experience and from truths in principle accessible to anyone. Theology, on the other hand, has its starting point in truths that God has revealed about Himself. What distinguishes theology from faith, according to Thomas, is that theology is a more or less sophisticated reflection on believed truths that brings to bear on them whatever we know from other sources. This is the sense of the traditional view that philosophy is the handmaid of theology. Philosophy, that is, all natural knowledge, is used by the theologian in his attempts to understand what he believes.
(Ralph McInerny, Ethica Thomistica: The Moral Philosophy of Thomas Aquinas, rev. ed. [Washington, DC: The Catholic University of America Press, 1997], 117)
