Abstract

The paper presents two objections against Putnam’s Twin Earth argument, which was intended to secure semantic externalism. I first claim that Putnam’s reasoning rests on two assumptions and then try to show why these assumptions are contentious. The first objection is that, given what we know about science, it is unlikely that there are any natural-kind terms whose extension is codetermined by a small set of microstructures required by Putnam’s indexical account of extension determination. The second objection is that there may not be a plausible concept of a speech community whose adoption would classify Oscar and Twin Oscar as members of different speech communities and, at the same time, render Oscar and Twin Oscar as being in the same psychological state. I contend that Putnam’s argument fails because both objections are justified.