能愿动词
Modal verbs

第四级里你已经说过这样的话：“我会说汉语”“我能来”“你可以走”“我想喝咖啡”“我要去北京”“你应该休息”。这六个词有一个共同点——它们都站在另一个动词前面，自己不表示动作。今天给这一类词起个名字：能愿动词。

You have been saying these since level 4: 我会说汉语, 我能来, 你可以走, 我想喝咖啡, 我要去北京, 你应该休息. All six words share one habit — each stands in front of another verb and never names the action itself. This lesson gives the class its name: 能愿动词.

能愿动词也叫助动词：它帮助后面的动词，说明这件事能不能、可不可以、想不想。它后面跟的是动词或者动词短语。“我会汉语”这样的句子也说，可是那时候“会”是一个普通的及物动词，意思是“掌握”，不是能愿动词。

The other name for the class is 助动词, auxiliary verb: it helps the verb behind it and says whether the event is possible, permitted or wanted. What follows it is a verb or a verb phrase. You will also hear 我会汉语 — there 会 is an ordinary transitive verb meaning 'to have mastered', not a modal.

“没”否定的是已经完成的事情，能愿动词说的不是一件已经发生的事，所以它的否定词是“不”。口语里能听到“昨天我没能去”，那是“没做到”的意思，否定的是整件事，不是能力本身。

没 negates a completed event, and a modal never reports a completed event — so the negator is 不. You will hear 昨天我没能去 in speech; there 没 is negating the whole event that failed to come off, not the ability itself.

“了、着、过”要放在后面那个动词上：不说“会了说”，也不说“想想去”。句尾的“了”是另一回事——“他会说汉语了”很自然，那个“了”管的是整个句子，表示情况有了变化：他以前不会，现在会了。

了, 着 and 过 belong on the verb behind the modal, never on the modal itself. Sentence-final 了 is a different animal: 他会说汉语了 is perfectly natural, because that 了 covers the whole sentence and reports a change — he could not before, and now he can.

“能”“可以”多半看客观的条件——外面的情况允许不允许；“想”“要”看主观的愿望——说话的人自己怎么想；“应该”在中间，说的是道理上该不该。还有一个“必须”，意思跟能愿动词很近，可是它不能单独回答问题，否定也不说“不必须”，要说“不必”“不用”，所以多数语法书把它归入副词。

能 and 可以 look outward at conditions and permission — the 客观 side; 想 and 要 look inward at what the speaker wants — the 主观 side; 应该 sits between them and talks about what is right. 必须 means much the same as a modal, but it cannot answer a question alone and its negative is 不必 or 不用, never 不必须 — which is why most grammars file it with the adverbs.