 Lewis does not think there is a once-and-for all correct answer to which respects of resemblance are relevant. He rejects the idea that things have primitive essences which somehow determine or constrain what is possible for them. Rather, it is ultimately up to us which respects of similarity we prioritize. Often this choice is not fully settled, leaving the counterpart relation vague and context-sensitive (see Lewis 1971, 209–11; Lewis 1973b, 41; Lewis 1983d, 42–3; Lewis 1986e, 251–5; Lewis 2003, 27–8).