ln "Possibilities and the Arguments for Origin Essentialism" Teresa Robertson (1998) contends that the best-known arguments in favour of origin essentialism can succeed only at the cost of violating modal common sense—by denying that any variation in constitution or process of assembly is possible. Focusing on the (Kripke-style) arguments of Nathan Salmon and Graeme Forbes, Robertson shows that both founder in the face of sophisticated Ship of Theseus style considerations. While Robertson is right that neither of the arguments is compelling (...) as formulated, each can be modified to fend off her particular counterexamples; these modifications do not differ in kind from those already needed to deal with ordinary Theseus cases, requiring only a further narrowing of the sufficiency clause from which the necessity of origins is derived. (shrink)