ought to ：
它比must語氣弱,但婉轉(zhuǎn).
They ought to be there by now.他們現(xiàn)在一定到那了
一般用于肯定和否定句
ought 與不定式構(gòu)成謂語動(dòng)詞.主要用法如下：
（ 1 ）表示應(yīng)該做某事.例如：You ought to take his advice.你應(yīng)當(dāng)接受他的勸告.
（ 2 ） ought + 不定式的完成形式,表示本應(yīng)該做某事.
例如：They ought to have handed in the paper yesterday.
他們本應(yīng)當(dāng)昨天交論文.
should ：
表示說話人的猜測(cè),估計(jì)應(yīng)該
That should be Janet coming upstairs now.正在上樓的準(zhǔn)是珍妮特.
多用于第一人稱.
should
(1) 表示勸告或建議.例如：He should learn how to drive the car.
(2) 表示預(yù)測(cè)或可能.例如：This kind of reference book should be in the reading-room.
(3) 表示驚奇、憤怒、失望等感情.例如：Why should I go?我干嗎要去?
(4) should + 動(dòng)詞的完成形式,表示應(yīng)該已經(jīng)做某事.例如：I should have thought of that.
(5) should + 動(dòng)詞的進(jìn)行形式,表示應(yīng)該正在做某事.
例如：You should be reading a textbook instead of the novel.
你現(xiàn)在讀的應(yīng)當(dāng)是一本教科書而不是那本小說.