American Catholic Philosophical Quarterly

Volume 92, Issue 4, Fall 2018

Daniel Shields
Pages 535-561

Everything in Motion is Put in Motion by Another
A Principle in Aquinas’s First Way

I argue for a novel reading of the mover principle used in Aquinas’s motion proofs for God’s existence. Many interpret Aquinas’s principle as holding that everything in motion is moved by something else currently in contact with it. Others, following James Weisheipl, understand the principle as claiming only that everything being moved is being moved by something else. I argue against both readings and hold that the principle means that everything in motion is moved by something else—whether that something else simply set it in motion or is currently moving it by contact. By looking closely at Aquinas’s inductive argument for the mover principle, I show that simultaneity between mover and moved is not necessary on Aquinas’s view. My interpretation allows me to respond to objections to Aquinas’s act-potency argument for the mover principle more convincingly than others, and sets the groundwork for robust engagement between Thomism and modern science.