Of these only four are generally recognized in poetical compositions:
(1) The Ping-sheng, or low and even note.
(2) The Shang-sheng, or sharp and ascending note.
(3) The Khü-sheng, or clear and far-reaching note.
(4) The Ruh-sheng, or straight and abruptly finished note.
These tones help to distinguish words which have the same phonetic sound but different meanings. For instance, the word—
'li' (Ping-sheng) = black.
'li' (Shang-sheng) = village.
'li' (Khü-sheng) = sharp.
'li' (Ruh-sheng) = strength.
In written Chinese each of these words is distinguished by a different character, and the tone is, therefore, of secondary importance; but occasionally a character has two tones—a ping and a khü, for instance, and then each tone indicates a difference of meaning, or distinguishes the use of the word as a substantive from its use as a verb.
But in poetry these tones are used to make rhythm as well as to express meaning, and when used for this purpose they are divided into ping and tseh, the ping representing the ping or low, even tone, and the tseh the other three tones, Shang, Khü, and Ruh. This brief explanation will enable the reader, I think, to perceive what is regarded by Chinese as the rhythm of a poem. In the diagrams given above, the first line consists of two ping tones, followed by three tseh tones, which are followed by two ping tones; and the arrangement of the characters in each line in terms of ping and tseh forms the rhythm of Chinese poetry. When compared, it will be seen that there are lines or couplets which are in contrast to, or harmonize with, other lines, &c.
But it is not necessary that the tones of all the characters in each couplet should agree, excepting the first and last lines which always agree exactly—tone for tone. In the other lines, the tones of the first, third, and fifth characters in a seven-character line, and the first and third in a five-character line, may be varied—ping for tseh, or tseh for ping; but the second, fourth, and sixth characters in seven-character poems, and the second and fourth in five-character poems must not be changed; when the ping tone should be used it must be used, the tseh may not be substituted for it, and when the tseh should be used it must be used, the ping may not be substituted for it. And when the opening tone of the first line is a ping, the opening tone of the line following must be tseh, and vice versa.