If ethical values are all commensurable, differing from one another only in quantity, what difference does this make? Plato gives us a stark and simple answer. The adoption of an ethical ‘science of measurement’, at the heart of which is the belief in commensurability, is both necessary and sufficient for ‘saving our lives’. Here I propose to examine one aspect of Plato’s ‘life-saving’ project: namely, some alleged connections between the belief in the commensurability of value and the nature of the human emotions. It is Plato’s idea, I shall argue, that the belief in commensurability cuts very deep: taken seriously, it will transform our passions as well as our decision-making, giving emotions such as love, fear, grief and hence the ethical problems that are connected with them, an altogether different character.
