||Two options or objects a and b are said to be incommensurable, incommensurate, or incomparable with respect to some value when the comparison is not malformed or irrelevant, but with respect to the value in question, (i) it is not true that a is better than b, (ii) it is not true that b is better than a, and (iii) it is not true that a and b are precisely equally good. A famous example (from John Broome) is the comparison between Stonehenge and Salisbury Cathedral: which is more impressive? Incommensurability raises two main sets of issues. First, what is the semantic and metaphysical status of a comparison between incommensurate objects? Second, how can practical reason operate when it must choose between such objects?