Graduated from Davidson College with a degree in philosophy. He received a master’s degree in classics from Brigham Young University. Subsequently he spent a year studying archaeology at the American School of Classical Studies in Athens, then completed a Ph.D. in philosophy at the University of Texas at Austin. After teaching at Grinnell College and Rice University, he came to Brigham Young University, where he is now professor of philosophy. His main area of research is ancient Greek philosophy. He is the author of Aristotle’s Two Systems (Oxford University Press, 1987), editor of the collected papers on ancient philosophy of Gregory Vlastos, Studies in Greek Philosophy, 2 vols. (Princeton University Press, 1995), and translator-commentator of Aristotle: Physics, Book VIII (Oxford University Press, 1999). He is a member of the board of editorial consultants of History of Philosophy Quarterly.