A second explanation is suggested by the material described in Rowlands' paper. Tone and intonation often become seriously intermeshed. Neither can be adequately systematized until we are able to separate the two and assign the observed phenomena individually to one or the other. Other pairs of phonologic subsystems also interact or overlap in this way; for example, duration sometimes figures in both the vowel system and the intonation. Some phonetic features, for example glottal catch or murmur, are sometimes to be assigned to segmental phonemics and sometimes to accentual systems. But no other two phonologic systems are as difficult to disentangle as are tone and intonation in some languages. This explanation of tone difficulties, however, does not apply in all languages. In some (the Ewe type mentioned above) interaction of tone and intonation is restricted to the ends of intonation spans. In many of the syllables, intonation can be safely ignored, and much of the tonal analysis can be done without any study of intonation. Still, even in such languages tone analysis has not been as simple as one might expect.

A third explanation is suggested by Richardson's analysis of Sukuma tone. There we see a basically simple phonemic system enmeshed in a very complex and puzzling morphophonemic system. While the phonemes can be very easily stated, no one is likely to be satisfied with the statement until phonemic occurrences can be related in some way to morphemic units, i. e. until the morphophonemics is worked out, or at least far enough that it seems reasonable to expect success.