Since ancient languages and modern languages have different pronunciations, how do poems rhyme?

Different times bet different rhymes. Analyzing syllables into two parts: sound and rhyme is an abstract process to analyze and summarize the syllables naturally produced in use. For ordinary people, in the process of speaking, syllables are already the smallest unit, so there is no need to analyze them. Therefore, the difference between phonological concepts is actually a great discovery. The ancients in China had an overall understanding of syllables. With the introduction of Buddhism into China in the Eastern Han Dynasty, Sanskrit classics were gradually brought into China. Sanskrit, on the other hand, is a phonetic symbol (recorded Sanskrit belongs to Indo-European language family), which is divided into consonants and vowels. Indians have long been aware of this. Inspired by Sanskrit, the ancient people in China gradually divided Chinese syllables into two parts: sound and rhyme. In the Southern Dynasties, Shen Yue wrote Four Tones Spectrum, put forward the theory of four tones and eight diseases together with several other literary celebrities, and summarized the influence law of tone in the formation of poetic rhythm beauty. These achievements have laid the requirements for rhythm and balance in modern poetry and promoted the emergence and development of modern poetry. With the requirements of rhyme and equality, poetry rhymes according to the "rhyme part" when writing poetry. I once asked, "Does ancient Chinese sound the same as modern Chinese?" The answer mentioned "rhyme book". The classification outline of these rhyme books when recording the pronunciation of Chinese characters is the current dictionary of "rhyme department". If you look up words according to "phonetic order", they are actually sorted according to the order of Chinese phonetic letters in English letters. But in the ancient rhyme book, it is different. They classify words according to vowels. Those with the same vowels belong to one category, and each category is called a "part". A poem must rhyme, and its rhyming words must be selected in a "rhyme department" to meet the requirements of rhyme. However, due to the change of pronunciation and the different division of phonological parts, the division of phonological parts is also different in rhyme books of different times. For example, Qieyun in Sui Dynasty is divided into 206 parts (each part is not too many words), which seems to be too detailed. In the Song Dynasty, Pingshui rhyme merged into 107, which was much less. This decrease in rhyme is not only due to the combination for simplicity and convenience, but also due to the change of pronunciation itself. In different times, there are different rhyming books and rhyming parts, and the requirements for rhyming will change slightly. Ancient poetry can be counted as rhyme if it conforms to the classification of rhyme when writing. From the stage of "modern Chinese" to the present, many scribes have deliberately insisted on writing poems according to the rhyme of Tang and Song Dynasties in order to be elegant, antique and even ancient. Even though the words at that time no longer rhymed, they rhymed because they matched the rhymes of the ancients. Since modern times, folk opera and folk art artists in the north have basically used "thirteen strokes" summarized according to the pronunciation of modern Chinese, that is, commonly used words are roughly divided into thirteen categories similar to rhyme (compared with this figure, it means that the 206 works mentioned above are "too detailed"), namely: Fahua, Sobo, Yin Xie, One-stop, Gusu and Quyi. The two words in each group are only representative words of rhyme chosen for convenience of memory, and have no special meaning. In order to make it easier to remember, artists use one word to represent the same story and put thirteen stories together to form a sentence: "The pretty woman twisted out of the room and sat in the east, west, north and south." As long as the rhyming words are arranged according to the "Thirteenth Avenue", the traditional operas in the north can be counted as rhyming. Now people in the north often say that jingles and jingles generally rhyme according to this requirement. It can be seen that the pronunciation of Chinese characters has changed greatly since ancient times, and the requirements for rhyme are also changing with the times. So many ancient poems don't rhyme today. For example, the example given by @lotus9 is that there are many similar examples. For example, "the wind is very strong, apes are whining, and birds fly home on the clear lake and white beach." For another example, "Haw answers haw, Mulan is weaving at home, but she can't hear the loom, only the woman's sigh." And so on, the pronunciation in Putonghua doesn't rhyme, but because the "living fossil" dialects like Hakka (Zhongyuan dialect close to 1000 years ago) retain more pronunciation information of ancient Chinese, people who read ancient poems may rhyme more. In short, whether it rhymes or not can't be reversed. In other words, we can't measure the past by modern standards. When the pronunciation changes, it doesn't rhyme. Standards are always changing, times are different and rhymes are different.