What kind of choices are open to us in the face of a moral dilemma? Such was the topic of Professor Susumu Cato’s talk on 28 October 2025, “Social Choice and Moral Dilemmas: An Axiomatic Exploration”, which served as the 2025 John Stuart Mill Lecture—an annual academic highlight among the students and staff at the John Stuart Mill College.
The John Stuart Mill Lecture is an annual event centred around a leading scholar from a field related to the Philosophy, Politics, and Economics (PPE) programme at the John Stuart Mill College. The Lecture brings the students and staff at the College in conversation with foundational and important contemporary ideas at the intersection of the three disciplines of PPE. In the past, the Lecture has been given by, among others, Peter Singer (Professor of Bioethics at Princeton University), Rainer Hegselman (Professor of Philosophy at the Frankfurt School of Finance & Managements), and Tom Casier (Chair in Global Politics of Europe at the University of Groningen).
The 2025 John Stuart Mill Lecture was delivered by Professor Susumu Cato from the Institute of Social Science at the University of Tokyo. Professor Cato has written extensively in various fields within and at the intersection of philosophy, politics, and economics, including, among others, social choice theory, welfare economics, normative ethics and political philosophy, public health, law and economics, and industrial organisation.
At the John Stuart Mill College, Professor Cato engaged staff and students in a lively axiomatic exploration of situations many encounter in their lives: moral dilemmas. Moral dilemmas are moral situations where the best one could do—for example, the best occupation one could choose to pursue—does not seem to be straightforwardly defined. Professor Cato invited the audience to ponder the strengths of the axiomatic approach in dealing with such dilemmas. The axiomatic approach entertains various, possibly intuitively appealing, properties that one’s choices may satisfy: for example, how what is best, according to a given procedure, may change or not when the options available to us expand or contract. As social choice theory—the science of the impossible—teaches us, it is often the case that no choice procedure satisfies even a very limited number of such properties.
Professor Cato’s talk was an entertaining, often personal, narration of such possibilities and impossibilities of choice. It was followed by a spirited informal discussion with PPE students on topics such as the strengths and weaknesses of the axiomatic approach or of the theorems of welfare economics as a justification for a free market system.