Occasionally we may find a phoneme which occurs in so few morphemes or types of social situation as to permit of such correlation: e.g. initial /ð/ in English (which occurs in a few morphemes—'the', 'there', 'then', etc.). In some cases morphological elements may be coterminus with phonological elements. […] Similarly, if we include among the phonological elements those segments which represent so-called gestural and onomatopoetic sounds, and which combine only rudimentarily with other segments, we will find that the segments are in effect also morphological elements: e.g. if the tongue-tip click written 'tsk' in English is considered a phonological element of English, we will find that it is restricted to a relatively small number of social situations and meanings. In all these special cases a phonological element will be found to have high correlation with classes of social situations.
- Harris (1951), a pag.187, n.66