The word ‘則’ started from the original meaning of ‘to divide’ and developed into the noun meanings of ‘law’, ‘norm’, and ‘model’, and through the linguistic phenomenon of verbification, which was a common linguistic phenomenon in ancient Chinese, its meaning naturally expanded to mean ‘to take as a law’ and ‘to follow from’. In general, when it takes the form of “A則B,” B is usually filled with the meaning of common sense, norms, or beliefs that A takes for granted, either subjectively or objectively. “Regarding B as a law” implies “It is right to act and follow B as a law,” “It is natural,” “Use B as a basis,” etc. If the meaning of “regarding B as a law” is something that has already been put into practice or is being done, it means “A has already imitated B and is doing so or has become so.” Here, the adverbial meaning progressed again and developed into adverbial meanings such as ‘as it should be’, ‘of course’, ‘right away’, and ‘soon’. The use of adverbs develops again into statement markers, and in the “NP則VP” structure in the ≪左傳≫, ‘則’ can be said to be a statement marker in all cases except for some adverbial usages. The use of the conjunction ‘則’ develops in the statement marker, and when the preceding and following clauses form a typical descriptive sentence, ‘則’ appears to function as a conjunction.