His research is mainly in ancient Greek and Roman philosophy and ethics. He is the author of Stoic Cosmopolitanism (Cambridge U.P., forthcoming) and essays on a wide range of ancient Greek and Roman philosophy. In addition to the essays listed below, he has recently contributed chapters to Blackwell's Companion to Ancient Philosophy, Companion to Socrates, and Companion to Greek and Roman Political Thought; to The Cambridge Companion to Epicureanism and The Cambridge Companion to Greek Political Thought; and to The Routledge Companion to Ancient Philosophy.
"The Unity of the Soul in Plato's Republic." in Plato and the Divided Self, ed. Rachel Barney, Tad Brennan, and Charles Brittain (Cambridge: Cambridge U.P., 2012), 53-73.
"Contemplative Withdrawal in the Hellenistic Age." Philosophical Studies 137 (2008): 79-89.
"Wishing for Fortune, Choosing Activity: Aristotle on External Goods and Happiness." Proceedings of the Boston Area Colloquium in Ancient Philosophy 22 (2006): 221-256.
"Minding the Gap in Plato's Republic," Philosophical Studies 117 (2004): 275-302
"Epicurus on Friendship (Sententia Vaticana 23)," Classical Philology 97 (2002): 68-80.
"Justice and Compulsion for Plato's Philosopher-Rulers." Ancient Philosophy 20 (2000): 1-17.
"A Defense of Plato's Argument for the Immortality of the Soul at Republic X.608c-611a." Apeiron 30 (1997): 211-238.