為什么不用ought to?這也許是人們習(xí)慣了,覺得這么讀順口.如果你非要用ought to 也不是不可以.下面是這兩個單詞之間的區(qū)別,僅供參考：
should與ought to的比較
(1) 除表示“萬一”“竟然”等只能用should外,表示“應(yīng)該,應(yīng)當(dāng)”“可能”等,兩者可互換,只是ought to的語氣稍重.如：
You ought to/should work harder than that.你應(yīng)當(dāng)更努力地工作
She ought to/should finish it by next week.下星期她可能完成了.
You ought to/should have told him about it earlier.你本應(yīng)該早點(diǎn)把這件事告訴他的.
You oughtn’t to/shouldn’t have wasted time like that.你本不該像那樣浪費(fèi)時間的.
(2) should 強(qiáng)調(diào)主觀看法,而 ought to 強(qiáng)調(diào)客觀要求.如：
We ought to go and see my mother in hospital tomorrow,but I don’t think we will.我們按理應(yīng)當(dāng)在明天去看看住院的母親的,但我主認(rèn)為我們不會去.
(3) 在公告、須知或條例中,出于禮貌,常用should.如：
You shouldn’t run alongside the swimming pool.不準(zhǔn)在游泳池邊奔跑.
(4) 在虛擬語氣中只能用should.如：
He suggested that I should go there.他建議我去那里.
(5) 注意ought to的否定式與疑問式.如：
You ought not to do it.你不應(yīng)該做此事.
—Ought he to start now?他現(xiàn)在該動身了嗎?
—Yes,he ought (to) .是的,該動身了.
They ought to go now,oughtn’t they?他們現(xiàn)在該走了,對嗎?