Possible Worlds and the Necessary A Posteriori

W. V. Quine's famous objection to essentialism has provoked two responses. The unfriendly response is that it conflates the de re and the de dicto. The friendly response does not dispute the point about conflation but argues that, behind Quine's argument, lies an important epistemological problem for essentialism. This chapter argues that the problem can be solved by looking at the issue through the lens of possible worlds approaches to modal questions. This serves as a preamble to addressing the corresponding issue for the necessary a posteriori. There is an important epistemological problem for the necessary a posteriori but the possible worlds approach to modal questions offers a solution to it. The solution turns out to be version of twodimensionalism about the necessary a posteriori.