 The key claim is that there are some pairs of options for which it is false that one is preferred to (or better than) the other, but it is also false that they are equi-preferred (or equally good). Proposed examples include both the mundane and the serious: a Mexican restaurant and a Chinese restaurant; a career in the military and a career as a priest; and, in an example due to Sartre (1946), whether to stay with one’s ailing mother or join the Free French. Taking up the second of these examples: it is not the case that a career in the military is preferred to (or better than) a career as a priest, nor vice versa; but it is also not the case that they are equi-preferred (or equally good). Call the relation that holds between options in these pairs incommensurability.