体：汉语没有时态
Aspect, not tense

第四级里你学了四个小字：了、过、着、在。你会说“我吃了饭”“我去过中国”“门开着”“他正在看电视”。你可能一直以为它们是过去、现在、将来——不是。它们说的不是事情什么时候发生，而是说话的人从哪个角度看这件事。这个角度，语法上叫“体”。

Level 4 gave you four small words: 了, 过, 着, 在. You can already say 我吃了饭, 我去过中国, 门开着, 他正在看电视. You may have quietly filed them as past, present and future — they are not. They do not say when something happened; they say from what angle the speaker is looking at it. That angle is 体, aspect.

英语的动词要变：go, went, will go。汉语的“去”永远是“去”，一个字，一个样子。第一级到第六级你说了几千句话，从来没有变过一个动词，就是因为汉语根本没有这套东西。

An English verb changes shape: go, went, will go. Chinese 去 is 去 for ever — one character, one form. You have said thousands of Chinese sentences since level 1 without ever changing a verb, and that is not luck: the machinery simply is not there.

时间词是副词性的成分，位置在动词前面，常常放在句子最前面或者主语后面：“昨天我去公园”“我昨天去公园”都对。有了时间词，句子就清楚了；没有时间词，上下文也能告诉你时间，所以汉语很少说错。

A time word behaves like the adverbs of the last lesson: it stands before the verb, either at the very front or right after the subject — 昨天我去公园 and 我昨天去公园 are both fine. Once it is there the time is settled; when it is absent, the surrounding talk settles it instead.

四个体标记回答的是四个不同的问题：完成了没有？经历过没有？还是那个样子吗？正在进行吗？还要记住一点：不是每个句子都要体标记。经常发生的事、一般的道理、简单的描写，都不用——“我每天七点起床”“他是老师”“北京很大”，一个标记也没有。

The four markers answer four different questions: finished or not? ever done or not? still that way? happening right now? And one more thing to hold on to — most sentences need no marker at all. Habits, general truths and plain description take none: 我每天七点起床, 他是老师, 北京很大.

这句话是全课最重要的一句。“了”说的是“这件事完了，下一件事才开始”，至于这两件事在昨天还是在明天，由“明天”这个词决定，跟“了”没有关系。所以千万不要把“了”翻译成过去式。

This is the sentence to remember. 了 says one thing only: this event wraps up before the next one starts. Whether the pair sits in yesterday or tomorrow is decided by 明天, not by 了. Never translate 了 as a past tense.