My work is in the area of ancient Greek philosophy, specializing in Socrates, Plato, the Socratic schools, and Hellenistic Philosophy. My first book is a critical edition with translation and commentary of Philodemus: On Choices and Avoidances (Bibliopolis Press, Naples, 1995), a text of late Epicurean ethics. My analysis focuses on the topics of rationalism, attitudes towards superstition and the fear of death. I discuss the contribution of late Epicureans to practical ethics and explain its philosophical interest.

My second book The Epistemology of the Cyrenaic School (Cambridge University Press, Cambridge UK, 1998) is an interpretation of the epistemology of the Cyrenaics, a Socratic school active in the Classical and Hellenistic periods. I argue that the subjectivism of this school in some ways pre-announces modern positions and that its scepticism comes close to modern scepticism about the external world. Among the topics I examine are the relation between the mental and the physical, the authority of first-person reports, scepticism towards the empirical world and towards other minds, and the relations between relativism and scepticism.

My third book The Ethics of Philodemus (Oxford University Press, Oxford, 2006) reconstructs and assesses the ethical system of Philodemus, a very important Epicurean philosopher of the 1st century BC., whose surviving writings belong to the collection of the Herculaneum papyri.

I most recently published a book on Plato's Charmides (Cambridge University Press, Cambridge UK, 2022) and co-edited with Gabor Betegh the book Conceptualising Concepts in Greek Philosophy (Cambridge University Press Cambridge UK, 2024). Currently I am working on aspects of Aristotle’s metaphysics and ethics, Hellenistic and Roman philosophy, and a book on Plato's Republic Books 8-9.