 A third and final worry for Geach concerns his denial of absolute identity. As many commentators have pointed out, this denial has drastic implications for logic, semantics, and set theory. To take just one example, consider the set theorist’s axiom of extensionality: for any sets A and B, if A and B have the same members, then A is the same set as B. Let A be David’s unit set and let B be Lump’s unit set. Is A the same set as B? The relativist must reject this question as ill-formed. It makes no sense to ask whether x and y are the same members, since this requires a notion of absolute identity (intuitively, ‘member’ does not denote a genuine kind, so ‘same member as’ does not express a relative identity relation). As a result, the relative identity theorist must deny extensionality, which throws set theory into jeopardy (Hawthorne 2004).