The analysis of tone phonemes, or tonemes, like that of segmental phonemes, necessarily involves considerations of phonetic similarity—necessarily, because there is no other basis upon which tones occurring in noncontrastive distribution can be phonemically identified with one another. But how is ‘phonetic similarity’ to be understood in the case of tones? Not, certainly, in the sense in which it is understood in the case of segmental phones, where it denotes some objective similarity in the articulatory or acoustic characteristics of the phones themselves. To be sure, even in this case phonetic similarity is a rather elastic criterion; but at least it can be shown, for example, that two vocalic phones have a common tongue position, or two consonantal phones certain common distinctive features. No such objective similarity is demonstrable in the case of tones—at least, of level tones; for, since it is relative rather than absolute pitch that is involved in tonemic systems, a given toneme may occur at virtually any pitch of which the voice is capable. Variants of a man's high tonemes may be acoustically similar to those of a woman's low tonemes; and in the speech of a single speaker a given level of pitch in two utterances or even within one utterance may represent variants of several different tonemes. The possibilities of phonemic overlapping of level tonemes are virtually unlimited.