18.22. Successively Enclosing Constructions [...] It is possible to investigate the relation of each construction type to longer constructions which enclose it, and to the whole utterance in which it is contained. A step in this direction is taken when we state whether a construction contains free or bound forms; for this means that members of the construction sometimes or never constitute by themselves the whole utterance in which they are contained. Or we can say that almost all English utterances contain at least one of the free classes ('A, N ¹, V ¹, D', etc.) or the bound class 'S' […], with zero or more morphemes of the other bound classes ('Na', several 'T' and 'P', etc.) grouped around each of these. If each of these free classes, and the sequence of bound classes 'S + E', each with or without any of its accompanying bound classes, is not divisible into smaller sections which occur as complete utterances, then each of these constructions satisfies the two conditions for being a minimum utterance of the language.
- Harris (1951), a pag.329