Daily Inspiration Quote by Thomas Aquinas

Thomas Aquinas claims that God's existence can be demonstrated, but not by pure reason starting from definitions; it must be shown from effects available to experience. A priori demonstration would move from what something is to the fact that it is. Because we do not possess a direct grasp of God's essence, such a route is closed. Instead, Aquinas turns to a posteriori reasoning, the kind that begins with things more surely known to us: the changing, contingent, ordered world we encounter through the senses.

This epistemic posture reflects his Aristotelian conviction that human knowledge starts in sense experience. From effects that fall within our understanding, the mind can reason back to a cause. Aquinas calls such arguments demonstration quia, showing that something exists by tracing observable features to their ultimate source. His Five Ways exemplify this method: from motion to an unmoved mover, from efficient causes to a first cause, from contingent beings to a necessary being, from degrees of perfection to a maximal exemplar, and from goal-directed processes to an intelligent governor. These do not deduce God from a definition, as in Anselm's ontological proof, but infer God as the necessary explanatory terminus for features of the world.

The phrase more surely known to us marks a careful balance. Created effects are proportioned to our intellect; they can ground genuine knowledge that God is. Yet such knowledge remains limited and analogical. From effects we can attribute certain perfections to God and deny creaturely limitations, but we do not comprehend what God is. In the Summa theologiae I, q. 2, Aquinas distinguishes what is self-evident in itself from what is self-evident to us, and situates natural theology accordingly. He charts a middle path between rationalism that would define God into existence and skepticism that denies reason any purchase on the divine, grounding the ascent to God in the world we most securely know.