The search for restricted sequences, therefore, leads us not only to extract particular phonetic features, but also to repeat the extraction in some cases. We may thus break any sequences of tone, or of any other feature, into two simultaneously-occurring contours, if we can thereby analyze many different component sequences as being varying combinations of a few contours. We then say that the two contours were superposed upon one another.
- Harris (1951), a pag.51

When we test the extraction of various features which comprise a contour, we may find that some of the putative contours extend not over whole utterance but over many separated utterances. In an argument, for instance, one or all of the participants may speak loudly and with high pitch (or, given a different culture or personality, slowly; with low pitch and fortis articulation); these tone and stress features continue over many utterances in that conversation, and are superposed upon the previously-described utterance contours.
- Harris (1951), a pag.55