Possible-worlds talk obscures, rather than clariﬁes, the debate about haecceitism. In this paper I distinguish haecceitism and anti-haecceitism from other doctrines that sometimes go under those names. Then I defend the claim that there are no non-tendentious deﬁnitions of ‘haecceitism’ and ‘anti-haecceitism’ using possible-worlds talk. That is, any deﬁnition of ‘haecceitism’ using possible-worlds talk depends, for its correctness, on a substantive theory of the nature of possible worlds. This explains why using possible-worlds talk when discussing haecceitism causes confusion: if the parties to the discussion presuppose different theories of the nature of possible worlds, then they will mean diﬀerent things by ‘haecceitism’.