The Economist’s Johnson blog has an excellent post about the problem of defining exactly what a word is, anyway.
What is a word? The question might seem easy. One answer is that the list of all words in a language can be found in a dictionary. A second, commonsense definition, might be that everything that appears between spaces on a written page (such as this one) is a word. A third idea might be that words are the unsplittable building blocks of a language.
It might then seem surprising that for linguists—the academics who ponder what language is for a living—the definition of a word is not at all clear. It would surprise the average reader that many linguists do not much care for the idea of “words” as such. All three commonsense definitions above are so flawed as to be unusable.
(Read the rest.)
For a more in-depth treatment of the same topic, Heidi Harley has posted online the first chapter (“What is a word?”) of her textbook, A Linguistic Introduction to English Words, which is a fun read, especially for a textbook.