Function word

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In linguistics, function words (also called functors)^[1] are words that have little lexical meaning or have ambiguous meaning and express grammatical relationships among other words within a sentence, or specify the attitude or mood of the speaker. They signal the structural relationships that words have to one another and are the glue that holds sentences together. Thus they form important elements in the structures of sentences.^[2]

Words that are not function words are called content words (or open class words, lexical words, or autosemantic words) and include nouns, most verbs, adjectives, and most adverbs, although some adverbs are function words (like then and why). Dictionaries define the specific meanings of content words but can describe only the general usages of function words. By contrast, grammars describe the use of function words in detail but treat lexical words only in general terms.

Since it was first proposed in 1952 by C. C. Fries, the distinguishing of function/structure words from content/lexical words has been highly influential in the grammar used in second-language acquisition and English-language teaching.^[3]