Alexander against Galen on Motion: A Mere Logical Debate?

The debate between Alexander and Galen on Aristotle’s argument in Physics VII.1 that anything that moves is moved by something is currently understood as restricted to the question of the validity of this argument. This article questions this understanding and argues that (1) this debate directly bears on the tenability of the thesis that Aristotle’s argument establishes, and (2) it is rooted in an even more fundamental disagreement over hylomorphism and efficient causality. In substantiating these conclusions, the article examines Galen’s argument against Aristotle in light of his notion of dunamis and his account of antecedent causes. It also analyses fragments from Alexander’s lost commentary on the Physics, where the validity of Aristotle’s argument in Physics VII.1 is directly discussed and shows that he addresses Galen’s criticism through the view found in his De anima and elsewhere that substantial forms are causal factors and that external causes are the primary efficient causes.