Words and Lexemes

It is surprisingly difficult to define the word word, yet it is a necessary starting point for morphology. A workable definition comes from Lieber's Introducing Morphology (2009): a word is one or more morphemes that can stand alone in a language. This is a very simple definition, and what it means to "stand alone" is itself a large question.

Crucially, standing alone is not an orthographic matter. What can be written as a single word does not settle the issue, since many languages are unwritten and written language is not always the best reflection of what happens in the mind. The notion nonetheless matches ordinary intuition that a word is something able to stand on its own, and this is usually made precise phonologically, in terms of something like stress.

The lexeme

A word contrasts with a lexeme. A lexeme is a family of words that differ only in their grammatical endings or grammatical forms, such as the singular and plural forms of a noun, or the present, past, and participle forms of a verb.

Take walk, walks, walked, and walking. Depending on how one defines word, these could be counted as four different words. They are, however, only one lexeme. The differences among them lie in inflectional morphology, not derivational morphology. The word walk is formed using whatever derivational morphology the language provides, and it can then be inflected in various ways: the -s ending, the -ed ending, and the -ing ending each contribute a certain meaning and yield a different interpretation, but none of them changes the lexical meaning of the word. The result is still the same lexeme.

The practical upshot is a division of labor. If walk and walks both appeared in a sentence, most people would count them as two different words, even though they are one lexeme. The formation of lexemes is the domain of derivational morphology, while the family of forms a lexeme generates belongs to inflectional morphology. Understanding how lexemes are formed is therefore the entry point into derivational morphology.