完句是汉语研究中一个比较热门的课题，学者们经过研究，总结出来的完句范畴有如下一些：程度范畴、语气范畴、时间范畴、情态范畴、数量范畴、意愿范畴、否定范畴等。本文选取诸多完句范畴中的一个——时间范畴——进行详细考察，认为时间范畴对不同句子起作用的方式是不一样的。现实句表达已经发生或正在发生的情境，必然同特定时间发生联系，因此必须具备时间性才可完句，尤其是要提供内在时间（动词的“体”），指明动作处于时间进程中的何种阶段。外在时间（动词的“时”）于现实句的成立则是可有可无的。汉语是体突显的语言。非现实句，包括将来句、祈使句、惯常句、情态句等，表达的是尚未发生的、只存在于想象领域的情境，不同特定时间发生联系，因此不具备时间性也可完句。文章最后提到，这是汉语完句的一般规律，于规律之外也存在一些例外。例如，当动词带补语、修饰性状语、谓词性宾语时，即使句子表达现实情境，动词也可不带“了、着、过”等完句成分；报刊、杂志、网站的新闻标题中动词也常常不带体标记。对这些例外情况，文章尽可能地给出了解释。

Sentence completion is a hot topic in the study of the Chinese language. Researchers study at it and find many factors which may play a role in the completion of a sentence: degree, tone, time, modality, quantity, wish, negation, and so on. This paper chooses one factor and researches on it in length. We find that time affects different sentences in different ways. Sentences expressing realis tell about things that have already happened or are happening, which are surely confined to a certain point of time. Therefore, this kind of sentences must show the factor of time clearly, especially the inner time(the “aspect” of verbs). The outer time, however, is optional. Chinese is an aspect-prominent language. Sentences expressing irrealis, including future, imperative, habit and modality, are not confined to a certain point of time, thus can be said as a complete sentence without showing time. This is an important law of the Chinese language, but as usual, there are exceptions. For example, when the object of a verb is predicative, the sentence can stand without words indicating “aspect” such as “了(le)、着(zhe)、过(guo)”, even if it expresses realis. The paper also tries to give explanations for these exceptions.