Equative Sentences: Linguistic and Philosophical Perspectives

Equative sentences like Hesperus is Phosphorus are interesting not only because they convey information about identity but also because of the atypical linguistic means they employ to do so. An equative sentence appears to be composed of a pair of referential singular terms (grammatical arguments) and to lack a logical predicate. Yet in the absence of such a predicate, how can equatives constitute well-formed, meaningful sentences? This rarely acknowledged problem of symmetry is assumed to have an obvious predicativist solution, according to which equatives would actually contain some predicative constituent(s). We expose the problem of symmetry, critically review various predicativist solutions, and outline an alternative hypothesis according to which equatives are distinctive both syntactically, by virtue of their symmetrical [DP DP] structure, and semantically, by virtue of their meaning corresponding to an instruction to perform a mental act of identification rather than to a traditional predication (the ascription of a property or relation).