英語語法：情態動詞+ have +過去分詞+詞彙比較用法
高二是高中學習的關鍵時期，不僅課程任務重，而且很大程度上決定着學生今後的發展方向，以及能否考入理想的大學。有着豐富教學經驗的老師，向大家傳授高二各學科學習技巧，希望對高二學生掌握良好的學習方法、提高學習效率有所幫助。以下是英語學科的主要學習方法。
英語詞彙用法比較：have to與must，can與be able to
比較have to 和must的用法
1) 兩詞都是'必須'的意思，have to 表示客觀的需要， must 表示說話人主觀上的看法，既主觀上的必要。
My brother was very ill, so I had to call the doctor in the middle of the night. 我弟弟病得很厲害，我只得半夜裏把醫生請來。(客觀上需要做這件事)
He said that they must work hard. 他說他們必須努力工作。(主觀上要做這件事)
2) have to有人稱、數、時態的變化，而must只有一種形式。但must 可用於間接引語中表示過去的必要或義務。
He had to look after his sister yesterday.
3) 在否定結構中： don't have to 表示"不必"
mustn't 表示"禁止"，
You don't have to tell him about it. 你不一定要把此事告訴他。
You mustn't tell him about it. 你一定不要把這件事告訴他。
比較can 和be able to
1)can could 表示能力;可能 (過去時用could),
只用於現在式和過去式(could)。be able to可以用於各種時態。
They will be able to tell you the news soon. 他很快就能告訴你消息了。
2)只用be able to
a. 位於助動詞後。
b. 情態動詞後。
c. 表示過去某時刻動作時。
d. 用於句首表示條件。
e. 表示成功地做了某事時，只能用was/were able to， 不能用could。
He was able to flee Europe before the war broke out.
= He managed to flee Europe before the war broke out.
注意：could不表示時態
1)提出委婉的請求，(注意在回答中不可用could)。
--- Could I have the television on?
--- Yes, you can. / No, you can't.
2)在否定，疑問句中表示推測或懷疑。
He couldn't be a bad man.
他不大可能是壞人。
1) may(might) have + done sth, can (could) have + done sth 表示過去，推測過去時間裏可能發生的事情。
Philip may (might) have been hurt seriously in the car accident.
Philip can (could) have been hurt seriously in the car accident.
2)must have +done sth，對過去時間裏可能發生的事情的推測，語氣較強，具有"肯定"，"諒必"的意思。
---Linda has gone to work, but her bicycle is still here.
---She must have gone by bus.
3) ought to have done sth, should have done sth
本應該做某事，而事實上並沒有做。否定句表示"不該做某事而做了"。
You ought to (should) have been more careful in this experiment.
He ought not to have thrown the old clothes away.(事實上已扔了。)
ought to 在語氣上比should 要強。
4) needn't have done sth 本沒必要做某事
I dressed very warmly for the trip, but I needn't have done so. The weather was hot.
5) would like to have done sth 本打算做某事
I would like to have read the article, but I was very busy then.
