‘Semantic externalism’ is the view that the thought and speech of internally identical subjects can have different contents, depending on facts about their environments. ‘Semantic internalism’ is the negation of this view. The details of these two views depend on the definition of ‘internal identity’. Katalin Farkas has shown that the traditional definition of internal identity as physical identity is too permissive: it misclassifies certain bodily states as internal. She has proposed defining internal identity as phenomenal identity instead. In the (...) critical part of my paper, I argue that Farkas’s proposal fails for being too restrictive: it misclassifies non-conscious mental states, most notably dispositional belief, as external. I consider two interpretations of Farkas’s proposal but conclude that neither succeeds, because each requires internal features to influence the subject’s phenomenal life in a way in which dispositional belief does not. In the constructive part of my paper, I consider dispositional identity as an alternative definition of internal identity. I argue that the dispositional-identity definition avoids the phenomenal-identity definition’s shortcoming and retains its main attraction, viz., that of securing the subjective indistinguishability that obtains between Twin Earth duplicates. My argument that it does the latter, however, faces potentially decisive obstacles. Thus, I retreat to a disjunctive proposal: internal identity should be defined either as dispositional identity or as dispositional-plus-phenomenal identity. I conclude by defending my proposal against a different charge that may be levelled against it, viz., that of misclassifying Cartesian dualism as an externalist theory of the mind. (shrink)