Couplet Rules
(1) The number of words in the upper and lower couplets must be equal, and repeated words cannot be used.
(2) The last sentence of the first couplet must be in oblique tone, and the last character of the next couplet must be in flat tone.
(3) The sentence patterns of the upper and lower couplets must be consistent (similar parts of speech and corresponding structures).
(4) The flat and oblique characters in the upper and lower lines must be opposite to each other. Where the upper couplet uses flat-sound characters, the second line must use oblique-sound characters, and vice versa (ping: flat-sound characters; oblique, oblique-sound characters, including (a character with three tones: 上, going, and enter).
(5) The meanings of the upper and lower couplets can be similar or opposite. They can only say one thing, or they may also say two things separately.
The antithesis between couplets and verses has a relationship of inheritance and evolution. The rhythm of verses and the principle of "no matter one, three, and five, but two, four, and six are clear" also apply to couplets. As for the number of words in each couplet, there is no limit, ranging from four, five, six, seven, eight, nine to several or hundreds of words, as long as there is something to say and it can be paired.