Words are not "actual" or "existing" in any objective sense. A list of actual words always involves a subjective element: they are words compiled in the mental lexicon of some individual or other, or in a dictionary produced by certain lexicographers or in a fixed corpus constructed in some more or less arbitrary way. The "actual" words of any of these sources will very likely coincide in large part with the actual words of the others, but perhaps never in totality. In other words, the notion of "actual" word is to some extent a fiction, although a convenient and necessary one if we are to count words and thereby measure productivity.
- Baayen & Lieber (2004), a pag.63