 It also functions indexically, by indexing its symbol type, since its use in context presupposes that such a type exists in the semantico-referential grammar in use in the communicative situation (grammar is thus understood as an element of the context of communication).So icon, index and symbol are not mutually exclusive categories—indeed, Silverstein argues, they are to be understood as distinct modes of semiotic function, which may be overlaid on a single sign-vehicle.This entails that one sign-vehicle may function in multiple semiotic modes simultaneously.