In the widest sense of the term, grammar is that complex set of relations. According to a recent definition, grammar is 'a device that specifies the infinite set of well-formed sentences and assigns to each of them one or more structural descriptions'. That is to say it tells us just what are all the possible sentences of a language and provides a description of them. This is no small task, but one that is well worthy of human study.        There are three characteristics of language that are important for the understanding of the nature of grammar: it is complex, productive and arbitrary.