Correspondeces, compositionality and grammar

My purpose is to present some basic notions of cognitive grammar (Langacker 1987; 1990; 1991 ), with special emphasis on the extent of semantic compositionality and the nature of grammatical dependencies. I will start by asking a very basic question that hardly anybody ever bothers to ask: Why should there be such a thing as grammar? The way we answer this question may well determine how we think about grammar and ultimately how we analyze it.