The procedure of 4.21 [On the Equivalence of Repetitions] enables us to equate two utterances (and their component segments) as repetitions of each other without knowing what variations of this type will appear […] to be related to junctures and morpheme boundaries. There we can treat by saying that the two utterances (e.g. 'Take one and inquest') differ in that one of them has an intermittently present segment which the other lacks. Intermittently present segments or variations are then such as occur in some but not all repetitions of an utterance. If we take two utterances which are distinguished from each other only by the presence of an intermittent segment in one which is lacking in the other, they will be equivalent to each other in some of their repetitions and not in others.
- Harris (1951), a pag.40