To make this informal description of the interpretation of the type language precise, we turn to modal logic. Frames F = (W,R), in the categorial setting, consist of a set W of linguistic resources (expressions, ‘signs’), structured in terms of a ternary relation R. This ternary relation stands for grammatical composition, or ‘Merge’ as it is known in the generative tradition: read Rxyz as “the expression x is obtained by putting together the subexpressions y and z”. For comparison: in the Routley-Meyer semantics for relevance logic, R would be the accessibility relation interpreting the fusion operation.