_ Source: _Volume 55, Issue 4, pp 239 - 272 According to Peter Auriol, OFM, efficient causation is a composite being consisting of items belonging to three distinct categories: a change, an action, and a passion. The change functions as the subject bearing action and passion. After presenting Aristotle’s account of action and passion, which constitutes the background to Auriol’s theory of causation, this paper considers Auriol’s interpretation of Aristotle’s account in contrast to an alternative interpretation defended by Hervaeus Natalis (...) and William of Ockham. Finally, it shows how Auriol, on the basis of his interpretation of Aristotle, develops his own account of efficient causation as a composite being. (shrink)