本文將上古漢語中「則」的主要用法區分為兩類：一類是承接連詞，具有表示前、後依存關係的作用，可用於表示時間先後的承接複句、條件複句、推論複句、讓步複句的後一分句；另一類是話題焦點標記，具有標示話題焦點的作用，可用於話題闡述句、話題判斷句、話題釋因句的述題之前。從歷時演變的角度來看，兩類用法具有先後發展的關係：承接連詞「則」最早用於表示時間先後的承接複句，之後才擴大到條件複句或推論複句，並由條件複句擴大到讓步複句。而出現在條件複句裡的承接連詞又轉變為話題焦點標記，起初用於話題闡述句，然後再逐步擴大到話題判斷句、話題釋因句。

There were two major usages of zé（則）in Old Chinese. The first was as a consecutive subordinating conjunction that could express dependence between the first clause and the second clause in complex sentences. It was further used in successive sentences that expressed the chronological order of the latter clause as well as in the latter clauses of conditional, inferential and concessive sentences. Second, zé was employed as a topic focus marker that could indicate topical focus and be used before the comments of three kinds of topic sentences, including “relevance,” “judgment,” and “cause.” From the perspective of diachronic evolution, there was a relationship of sequential development in these two types of usage. At first, the consecutive subordinating conjunction zé appeared in successive sentences that expressed chronological order. Afterward, it extended to conditional or inferential sentences. Finally, it expanded from conditional sentences to concessive sentences. Moreover, the consecutive subordinating conjunction in the conditional became a topic focus marker. At first, it was used in the topic sentence of relevance. Subsequently, it came to be gradually used in topic sentences of judgment and cause.