This article discusses what grammar is in terms of the relation between grammar on the one hand and semantics\|pragmatics on the other. It first suggests a clear distinction between grammar Ⅰ (GI) and grammar Ⅱ,the former being in nature the objective rules and regulations growing from the use of language and internallized into the cognitive structure of the language\|user,while the latter the results of the studies of GI,demonstrating itself in the form of theoretical grammars and grammatical theories.The article then argues that GI is but the formalization and procedualization,in a word grammaticalization,of the abstaction of the semantic\|pragmatical factors concerned.The article finally attempts a notion fo “functional metabolism” which means the compensation of grammatical function for semantic\|pragmatical function,or vice versa,and explains that functional metabolism grows out of the fact that grammatical function is in some sense the reflection of semantic\|pragmatical function.