According to linguists Anna Maria Di Sciullo and Edwin Williams in their 1987 monograph On the Definition of Word, "there are three different ideas of what a word is" (p. 1). One idea is that a word is a "morphological object," that is, it is an object that consists of one or more morphemes--a morpheme being the smallest grammatical unit in a language, like the word dog or the plural -s in English. Another idea is that a word is a "syntactic atom," that is, a word is the smallest unit used in phrases and sentences (syntax). The third notion is that a word is an unit of language that is listed in a sort of mental dictionary (the lexicon in linguistic parlance), what Di Sciuollo and Williams term a listeme. Each of these is a distinct concept of what a word is. In their monograph, Di Sciullo and Williams dissect these various notions of "word" in considerable detail.
Whether or not Di Sciullo and Williams are right in claiming that there are three (and only three) distinctive notions of "word," the fact that they can identify at least three different conceptions of "word" demonstrates that words are much more complicated than we may have realized. This complexity adds to the challenge of really understanding what language is. Moreover, it adds to the challenge of explaining where language came from. How could neo-Darwinian evolution, which generally is thought to begin with the simple and basic, have brought about such a complex entity as a word? In short, asking ourselves what a word is should lead us to some skepticism about the standard Darwinian explanation of the origins of language.
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