Among the commentaries on Aristotle's 'Nicomachean Ethics' produced in the Middle Ages, that of Richard Kilvington is one of the most thought-provoking. Kilvington adopts a unique perspective of argumentation in which he applies concepts and terminology from the fields of logic and physics to ethical dilemmas. This unprecedented approach allows him to formulate original solutions to various ethical problems. He concentrates on the will, moral weakness, the relationship between the will and prudence, the change of virtues and vices, and the nature of ethical objects. The presented commentary is a valuable record of the philosophical debates at Oxford in the 14th century.