Classical poetry, also called archaic style, is written according to the practice of ancient poetry, and its form is relatively free, and it is not bound by metrical rules. Judging from the number of words in poems, there are four-character poems, five-character poems and seven-character poems.
Metric poems refer to ancient poems after the Tang Dynasty, which are divided into quatrains and metrical poems. According to the number of words in each sentence, it can be divided into five words and seven words. Style and sentence patterns have certain norms, phonology has certain laws, and the changes in use also need to abide by certain laws.
Therefore, Thinking on a Quiet Night should be a five-character quatrain in metrical poems.