ought
ought只有一種形式，后面須跟帶to的動(dòng)詞不定式。Ought表示"有義務(wù)或必要"做某件事，還可表示"勸告"。如：.
You ought to follow the old man's advice.你應(yīng)當(dāng)聽那位老人的話。
You oughtn't to smoke so much.你不應(yīng)當(dāng)抽煙太多。
You ought to go to the clinic at once. You don't look well.你臉色不好，應(yīng)該馬上到醫(yī)務(wù)室去。
[注]ought表示"應(yīng)該"，語(yǔ)氣比should 強(qiáng)。
ought后加動(dòng)詞不定式的完成式時(shí)
指過去的動(dòng)作。如用肯定形式(ought to have done)，表示某一件事該做而未做，相當(dāng)于should have done。如用否定形式(ought not to have done)，則表示一件不該做的事情發(fā)生了，相當(dāng)于should not have done。如：
He ought to have done the exercise more carefully.這個(gè)練習(xí)他應(yīng)當(dāng)作得更細(xì)心一些。
I ought to have returned these books to the library last week. 我上星期就應(yīng)當(dāng)把這些書還給圖書館。
You ought not to have been so rude.你不該這樣粗魯。
You ought not to have taken his skates without asking him.你不該沒有得到他的許可就把他的冰鞋拿走。