課本中不會教你的[M]478　must，can，can't和may/might表示的“推測”

478　must，can，can't和may/might表示的“推測”

① must可以表示推測或推斷，意為“想必，一定，準是”。must表示推測時只用于肯定句中，把握較大，常是合乎邏輯發(fā)展的必然結果。

He must be very hungry；he has worked in the fields all the afternoon. 他整個下午都在田里干活，一定很餓了。

② 在疑問句中表示推測要用can（可能），在否定句中表示推測要用can't（不可能）。

Can they have got my letter？他們可能已經(jīng)收到我的信了嗎？

This red pencil can't be yours. Yours is a blue one. 這支紅鉛筆不可能是你的。你的鉛筆是藍色的。

It can't be Sam that tells the lie；it must be Bob. 一定不是山姆說了謊，一定是鮑勃。

③ may/might表示推測時，意為“可能，也許”，把握性沒有must大。這種用法的might不是表示過去時態(tài)，而是表示對當前情況的推測，語氣上更加委婉。

He may/might be a worker. 他也許是一個工人。

He must be a worker. 他準是一個工人。

This sentence may/might be wrong. 這個句子可能錯了。

This sentence must be wrong. 這個句子一定錯了。

He may/might be invited to the party. 他可能會被邀請參加晚會。

He must be invited to the party. 他肯定會被邀請參加晚會。

There may/might be something wrong with the car. 車子可能出毛病了。

There must be something wrong with the car. 車子準是出毛病了。

④ must，can，can't，may/might表示推測、推斷時，可以轉換為相應的復合句，形式為：

must→It's certain+that從句

can→Is it possible+that從句

can't→It's impossible+that從句

may/might→It's possible+that從句

It must be a big fish. 那一定是一條大魚。

It's certain that it is a big fish.

Can his words be true？他的話可能是真的嗎？

Is it possible that his words are true？

He can't be still working now. 他不可能現(xiàn)在仍在工作。

It's impossible that he is still working now.

He may/might be still worrying about it. 他可能仍在為那件事?lián)摹?

It's possible that he is still worrying about it.

比較

He must be over sixty years old. 他準有60多歲了。

He can't be over sixty years old. 他不可能有60多歲了。

Can he be over sixty years old？他會有60多歲嗎？

提示

注意不可說Yes，I need；作情態(tài)動詞用時，need通常用于否定句和疑問句，不用于肯定句，肯定句要用must。

A：Need I go there at once？我需要馬上去嗎？

B：Yes，you need.

B：Yes，you must.

I must get up early，but you needn't. 我必須早起床，但你不必。