According to the Biography of Liang Shu and Shen Yue, it is recorded that: "I wrote a four-tone score, thinking that in the past, poets were tired for thousands of years and didn't realize it, but they only got a chest, exhausted their wonderful intentions, and called themselves fascinated works. The emperor asked Zhou She,' What are the four tones?' Sheyue:' The sage of the son of heaven is also right.' "So, the name of" Ping, Shang, Qu and Jin "is determined. This traditional classification of tones into flat tones, rising tones, falling tones and entering tones according to their different pronunciation is called "Tone Category".
The rhymes of Sui and Tang Dynasties, and Guang Yun in Song Dynasty also divided the tones into four types, namely "Ping", "Shang", "Qu" and "Ru", which are called "Four Tones". Later, the four-tone system of this medieval period was largely retained in the pronunciation of various places. But language, whether it is pronunciation, words or grammar, will change with the advancement of the times.
in terms of tone, after Zhou Deqing's phonology in the Central Plains in the Yuan Dynasty, the "flat tone" of northern pronunciation has been divided into two categories, namely "flat tone" and "flat tone". The law of its evolution is generally as follows: the ancient sound belongs to the words with clear initials, which are all pronounced as "yin ping" in modern times; The ancient sound belongs to the word of voiced initial, which is pronounced as "rising tone" in modern times. This is why the "flat voice" of Beiping dialect is divided into "level tone" and "level tone". As for the three tones of "Shang, Qu and Ru" in other places, some of them are divided into yin and yang, so there are tones of "Yin Ping", "Yang Ping", "Yin Shang", "Yin Qu", "Yang Qu", "Yin Ru" and "Yang Ru", such as Chaozhou dialect. In some places, there is no distinction between yin and yang, such as Quanzhou dialect, Fuzhou dialect and Hakka dialect, so these dialects have seven tones each. Therefore, the tones of dialects vary from three (such as Luanxian County, Hebei Province) to as many as ten (such as Bobai County, Guangxi Province).
In a word, the tones of modern Chinese Putonghua can be divided into four categories, namely, "Yin level tone, Yang level tone, rising tone (reading as' appreciation') and falling tone", which are called Yin, Yang, rising tone and going tone for short. However, ordinary people or primary school students only use the first sound, the second sound, the third sound and the fourth sound instead of Yin, Yang, Shang and Qu.
In addition, the so-called rhyme is to classify words with the same vowel into one category, which is called rhyme. All the words in the same rhyme department are homonyms. Any poem requires rhyme, no matter ancient or modern, Chinese or foreign. The difference is that the restrictions on rhyme are more or less, strict and wide. This is also the biggest difference between poetry and other literary genres. More commonly used is "18 Pingshui Rhymes", see the previous article "On the Rhythm of Ancient Poetry" for details.