For instance, tones, or as some people call them tonemes, have exactly the same function as phonemes; they are distinctive, which means that the speaker, at a certain point of the message, will have to choose between a number of them in order to say just what he wants to say. It is, of course, perfectly immaterial whether the choice is conscious or not. If tones are not considered distinctive features of vocalic phonemes, it is because they are usually found to affect, not a vowel phoneme as such, but a syllabic nucleus, often made upon two or more phonemes or even more than one syllable.
- Martinet (1962), a pag.30