We may also find in some languages that loose contact and division between breath-groups of phonemes occur at morpheme boundaries, or that pauses occur sometimes (though not always) at morpheme boundary, but practically never within a morpheme. Such pauses could not be included in the phonemic content of the morpheme, except as intermittently present features in the utterance. They are free variants, and do not occur every time morpheme boundary occurs. But in some occurrences of the morpheme sequences those pauses would constitute observable evidence of morpheme boundary. In many cases, however, these pauses come at points containing phonemic junctures […]. At these points in the utterance we find segments which occur only at utterance boundary or at points of intermittently present pauses, and which are phonemicized into junctures or into sequences of some phoneme plus juncture. We can then say that the pause (when it occurs) is an occasionally-occurring free variant of the phonemic juncture.
- Harris (1951), Pag. 174

In addition to the phonemic features, constructions in some cases have phonetic boundary features which though positionally limited are not phonemic because they appear only occasionally, i.e. their occurrence is a free variant of their non-occurrence. 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.
- Harris (1951), Pag. 344