Thus pauses (for breath, for hesitation, for emphasis, for interruption, etc.) rarely occur within a morpheme, but in many languages will occur with increasing frequency at successively larger morphological boundaries. These are the intermittently present distinctions of the Appendix to 4.3, and one of the conveniences of setting up the domains of sequence resultants, components, and constructions is that it is these domains which usually correlate with the point of occurrence of these intermittently present elements.
- Harris (1951), a pag.345

Utterances and parts of utterances which do not occur in the same environment cannot be directly tested in order to see if they are or are not repetitions of each other […]. Even where the test is possible we may have an ambiguous result, in the case of features which appear in some repetitions of an utterance and not in others; these are the intermittently present distinctions of the Appendix to 4.3.
- Harris (1951), a pag.361, n.1

Phonemes, intermittently present distinctions, and morphophonemes are thus all defined as classes of corresponding segments, but under different conditions: […] intermittently present features are classes of substitutable segments in many repetitions of an utterance […].
- Harris (1951), a pag.362, n.3