Flat tone is the tone of Chinese pronunciation, flat tone, which used to be divided into flat tone and flat tone, which is equivalent to one and two tones in today's pinyin tone; In the past, there were three tones of rising, going and entering. The rising tone is equivalent to three tones of today's pinyin tone, and the falling tone is equivalent to four tones of today's pinyin tone. Rusheng, a tone, no longer exists in today's standard Putonghua. In the past, Rusheng characters have been allocated to the other four tones today, most of which are classified as flat tones.
As a poem, there are some differences in rhyming methods due to different genres. As we can see, the genre of five-character and seven-character in ancient poetry is that two five-character or seven-character sentences are combined into a complete sentence, which is called a couplet, and the end of each couplet rhymes. Moreover, the tones of rhyming characters must be consistent, that is, the flat sound and the flat sound are in harmony, and the falling sound and the falling sound are in harmony. Flat tones must not rhyme.
However, in some special cases, two sentences in a couplet need to rhyme-the place where a long poem (a short poem, which is extremely rare in the middle) changes rhyme, and the rhyme-changing couplet needs a new rhyme in the first sentence, a new rhyme in the second sentence, and then a new rhyme in each couplet. Secondly, it is the first sentence of a poem's first couplet, which is usually optional, mainly depending on the tone of the last word of the first sentence. If the tone of the last word of the first sentence is consistent with the tone of the whole poem, it must rhyme, otherwise, it is not necessary to rhyme.
This is the example in your question. Why do one or two sentences rhyme? Because the ending of the first sentence is flat, it must rhyme. Don't bet on the third sentence, because the third sentence and the fourth sentence are linked together, and the ending rhymes. Moreover, the flat tones of the upper and lower sentences in a couplet of metrical poems should correspond to each other, and the final word of the third sentence must be flat tones, which can't rhyme with flat tones.
Interpretation
In poems and songs, words with the same or similar vowels are used at the end of some sentences to make the tone harmonious and beautiful.
The so-called rhyme (also called rhyme and Ye Yun) means putting the words with the same rhyme in the specified position.
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 part are homonyms. Any poem requires rhyme, regardless of ancient and modern times, Chinese and foreign countries. 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 are 18 Pingshui Rhymes.
Rhyme is an important means to enhance the musicality of poetry. In order to make the tone harmonious and easy to remember, modern poetry is very particular about rhyme. The ancients usually used official books to guide rhymes, such as Tang Yun, Guang Yun, Libu Rhyme, Peiwen Rhyme, Poetry Rhyme Integration, Poetry Rhyme Together, etc. Among them, The Rhyme of New Publication written by Wang Wenyu in the Southern Song Dynasty is the most popular, which is called 18 Pingshui Rhymes by the world.
However, it needs to be understood that it is not worth destroying the nature of the poem to accommodate the rhyme. Unless you take part in the imperial examination, even if one or two sentences rhyme occasionally, the ancients are allowed.
Pingping the rhyme
In order to harmonize the rhyme, modern poetry generally pingping the rhyme, and most modern poems (that is, poems from the Tang Dynasty and later, called ancient poems before the Tang Dynasty) also comply with this requirement. However, there are still some typical works about the rhyme, such as Liu Zongyuan's five-character quatrain "Jiang Xue", the full text of which is entered into the tone (short sound): a hundred mountains and no bird, a thousand paths without a footprint; A boat on the river, a fisherman in his bagworm moths; Fishing alone, not afraid of snow and ice attack. No matter whether this poem is read with the rhyme ending of the ancient entering tone or with the rhyme of ie and ue in Putonghua today, there is no suspicion of a mouthful.
One rhyme to the end
In principle, rhymes cannot be changed in the middle of modern poetry, especially in the test poems, poems that should be made and poems with limited rhymes in the scientific examination room. However, due to the fact that the system of Qieyun used in scientific research is not completely in line with the spoken phonology of the Tang Dynasty, some vowels have been merged or separated, and it is even more likely that some poets can't change their local accents and use local accents to write poems, so there are still works that have been replaced by neighboring rhymes in their poems, such as Du Fu's My Ancestors:
I live in my old grandson and have a simple ancient style. When ploughing and chiseling, the clothes are the same as the world. Get up early at home, worry about your country and wish you a prosperous year. When it comes to the relationship between the monarch and the minister, the scriptures are full.
Note: The "wind", "the same" and "the middle" in the second, fourth and eighth sentences are flat-voiced and "east" rhymes, and the "feng" in the sixth sentence is flat-voiced and "winter" rhymes.
Writing poems every day is different from taking an exam, so we should not treat the authors harshly, especially those who use ancient rhyme books to write poems in the future.