Verbal Behavior: Extended Edition. Chapter 2: General Problems. Quote 10

A long-standing problem in the analysis of verbal behavior is the size of the unit. Standard linguistic units are of various sizes. Below the level of the word lie roots and affixes or, more rigorously, the small “meaningful” units called morphemes. Above the word come phrases, idioms, clauses, sentences, and so on. Any one of these may have functional unity as a verbal operant. (p. 21)