What is clear nowadays, however, is that the morpheme concept is only of limited value. It can certainly display the minimal units of grammatical analysis n a vast amount of language data. The irregularities of English are not, after all, very many. And when it comes to the analysis of the agglutinative languages, the morpheme concept is invaluable, as these languages are, as it were, tailor-made for it . But when we consider the difficulties of morphemic identification as a whole, it is clear that the concept is not as all-embracing as it has sometimes been made out to be. When we consider other problems of identification, due to semantic variability, for instance, the situation gets even cloudier. Is "boy" in "Send the boy" (said by a shop keeper about a part-time assistant) the same morpheme or different from "boy" in "This is my boy" (said by a parent)? A glance at any dictionary would show how vast the problem of "semantic overlapping" is. As a result of such problems, there is no linguistic theory these days which is based primarily on the morpheme concept; but every linguist would recognize the existence of morphemic units in language and would try to make his theory take account of them in some way. Morphemes are viewed as the units that the grammatical rules of the language have to work on ---- the minimal, meaningful units which it is the purpose of grammar to organize onto the various structures which it contains. Putting this another way, for many linguists the inventory of morphemes in a language is the basis of that language's dictionary, or lexicon. The role of morphemes has thus changed considerably since they were first introduced into linguistic analysis; but they are still very much with us. --- David Crystal: Linguistics