TONE
So far this chapter has been mainly concerned with the major suprasegmental aspects of phonology (i.e., stress and intonation). There are, however, other linguistically important suprasegmentals like tone, length, and syllable.
The way pitch is used linguistically differs from language to language. In English, it does not much matter whether you say 'cat' with a high pitch or a low pitch. It will still mean "cat." In other words, tone does not change within a single syllable. Therefore, English is a non-tonal language. However, this is not the case in many languages. For example, if you say 'ba' with a high pitch in Nupe (a language spoken in Nigeria), it will mean "to be sour;" if you say 'ba' with a low pitch, it will mean "to count." Languages that use the pitch of individual syllables to contrast meanings are called tone languages (or tonal languages). In other words, tone refers to the changes of pitch within a single syllable that result in changes in meaning. Thai is a language that has contrasting pitches, or tones. The same string of "segmental" sounds represented by [na:] will mean different things when spoken with a low pitch, a mid pitch, a high pitch, a falling pitch from high to low, or a rising pitch from low to high:
In some tone languages the pitch of each tone is "level"; in others, the direction of the pitch (whether it glides from high to low, or from low to high) is important. Tones that "glide" are called contour tones; tones that do not are called level or register tones. In Thai, there are three level or register tones (low, mid, and high) and two contour tones (rising and falling). Since English is not a tonal language, this brief explanation of tone seems to suffice here.
