What tone does ancient poetry correspond to in modern times?

Flat tone is a tonal concept in rhyme. In ancient times, tones were divided into four types: flat tone, rising tone, falling tone and entering tone, among which the three tones of rising tone and entering tone were collectively called flat tone, which resulted in the concept of flat tone. There are four tones in modern Chinese: flat tone, rising tone, rising tone and falling tone, among which flat tone and rising tone are flat tones, while rising tone and falling tone are flat tones (which have a certain correspondence with ancient flat tones, but this is not what this article is going to talk about).

The requirement of flat words means that the syllables in a poem should be flat. Specifically, there are four kinds of flat and even words, which can be illustrated by Du Fu's poem "Jueju" (the following words belong to flat and even rhymes, and the following words are the same):

Careful readers will find that the third word in the third sentence is "ping" according to the requirement of ping, but the word "west" is flat. Why? It turns out that when the ancients set the rules, they also left room for change in poetry creation, that is, the first, third and fifth words can be even, but the tone stipulated in the sentence pattern is better.

The flat structure of all metrical poems is the combination of these four sentence patterns. The arrangement and combination are carried out according to the following rules of "circulation between sentences".