In this chapter we consider the conceptual basis of grammar. The sense in which we use the term 'grammar' here refers to the closed-class or grammatical subsystem: grammatical words and morphemes, and grammatical categories and functions. To claim that grammar has a conceptual basis is to claim that grammar is meaningful. As we observed in the previous chapter, one way of defining 'grammar' is on the basis of the qualitative distinction in meaning between open-class and closed-class elements. In this chapter, therefore, we are primarily concerned with the semantics of the closed-class elements. The reason for this emphasis is that, in recognition of the distinction between closed and open classes, linguists have traditionally defined the closed-class elements of language in terms of structure, function and distribution rather than in semantic terms. In contrast, the cognitive model assumes the grammatical subsystem can be semantically characterised along the same lines as the open-class subsystem. This view entails a continuum between open- and closed-classes within the inventory that represents knowledge of language in the mind of the speaker, rather than two sharply distinct knowledge systems. Of course, to claim that closed-class elements are meaningful is not to claim that they are conventionally associated with rich meaning in the way that open-class elements are. Recall the distinction that was introduced in the previous chapter between content meaning and schematic meaning (which is also known as structural meaning). In this chapter, we begin to explore the kind of meaning that cognitive linguists associate with closed-class elements.