can(could) may must 用法

情态动词can(could) may must 用法

1. must表推测只能用于肯定句式中，must不用于否定句式中和疑问句式中。

Eg. A) --- He reads and speaks English all the time.

--- He must like English very much.

B.) I didn’t hear the phone, I must have been asleep.

2. can表推测只能用于否定句和疑问句中。

Eg. A) This can not be done by him.

B) Mr. Bush is on time for everything. How can it be that he was late for the opening ceremony?

can用于肯定句式表理论上的可能性，不表主观推测:

Eg. 1) Accidents can happen on rainy days.

2) The World Wide Web is sometimes jokingly called the World Wide Wait because it can be very slow.

3. could表推测可用于肯定句，否定句和疑问句式中：

Eg. 1)---I have taken someone else’s green sweater by mistake.

--- It could be Harry’ s. He always wears green.

2) You couldn’t have left it on the bus, have you?

3) My cell-phone has disappeared. Who could have taken it away?

4. may/might表推测用于肯定句和否定句式中：

Eg. 1) This could/may/might be done by him.

2）Peter may/might come with us tonight, but he isn’t sur

e yet.

3）---I don’t really like James. Why did you invite him?

---Don’t worry. He might not come. He said he wasn’t certain what his plans were.

5. should表合乎情理的推测,多用于预期推测。

Eg. --- When can I come for photos? I need them tomorrow afternoon.

--- They should be ready by 12:00 .