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5．　 在有些動詞如：suggest、insist、order等動詞后，從句謂語動詞用“should + 動詞原形”，should可以省略。例如：

He suggested that we (should) discuss the problem right now.

4．　 動詞wish后的賓語從句中，謂語動詞可用過去式、過去完成式或would、might加原形。

例如：I wish I were as strong as you.

He wished I would stay with us.

She wished I had attended the meeting yesterday.

3．　 表示與將來事實相反的謂語形式。

例如：If they came tomorrow, we would told them about it. (In fact, they won’t come tomorrow。)

2．　 表示與過去事實相反的謂語形式。

例如：If I had left a little earlier, I would have caught the early bus. (In fact, I didn’t catch the bus.)

虛擬語氣表示說話人的意愿、假設、猜測或建議。虛擬語氣不表示客觀存在的事實，謂語動詞用特殊的形式表示虛擬語氣。

1．　 表示與現在事實相反時的謂語形式。

例如：If Tom were hungry, he would eat the bread. (In fact, Tom isn’t hungry.)

4. must與have to比較

must側重于個人意志和主觀上的必要，have to側重于客觀上的必要。如果用于過去時態或將來時態時，則要用have to的相應時態來代替must。但must可用于間接引語中表示過去的必要或義務。

My brother was very ill，so I had to call for the doctor in the middle of the night.

我弟弟病得很厲害，我只得半夜里把醫生請來。(一般過去時)

I haven't got any money with me，so I'll have to borrow some from my friend.

我身上沒有錢，只好向朋友借點了。(一般將來時)

He said that they must work hard.他說他們必須努力工作。

3. have to的疑問句

句型：Do(Does, Did, Will)+主語+have to +動詞原形？

Do you have to study maths now？

你現在必須學數字嗎？

Yes，I do.是的，必須學。

No，I don't(have to)。不，不必學。

Did he have to ask the question？

他非要問那個問題嗎？

Yes，he did.是的。

No，he didn't(have to).不。

2. have to的否定句

句型：主語+don't(doesn't, didn’t, will not)have to+動詞原形

You don't have to walk so fast.

你不必走那么快。

He will not have to buy a new coat next year.

明年，他沒必要買新外衣了。

1. have(has)to +動詞原形

have(has)to后面要用動詞原形。當主語為第三人稱單數時用has to，當句子是過去時用had to。

We have to leave now.

我們不得不現在就離開。

He has to work on Sunday.

他不得不在周日工作。

I had to do my homework last Sunday.

上周日，我不得不做作業。

2.表示推測的用法

can , could ,may ,might ,must 皆可用來表示推測，其用法如下：

a．could ,might 表示推測時不表示時態，其推測的程度不如can ,may。

b．can ,could 用于否定句和疑問句中。

句型：主語+ can't , couldn't +be +動詞ing．(否定句)

Can ,Could +主語 +be +動詞 ing．(疑問句)

They can't be cleaning the room now．他們現在不可能在打掃房間。

c．may ,might , must 用在肯定句中。

句型：主語+ may ,might ,must +be +動詞 -ing

(表示對現在發生動作的推測)

He must be sleeping . 他現在肯定在睡覺。

d．但如果上述這些詞 (must ,can't… ) + have +過去分詞則指對過去已發生的事進行推測。

The road is wet. It must have rained last night .

地是濕的；昨天晚上肯定下雨了。

There isn't any water on the road . It (can't ) couldn't have rained last night .

地面上一個水滴都沒有，昨天不可能下雨了。

(四) have to的用法