英语语法简单学：情态动词

【上期回顾】

英语语法简单学：介词

【本期内容】

一、内容纲要

二、内容简述

（一）定义

英语中的情态动词是用来表达必要性、可取性和确定性的程度的辅助性动词。

（二）基本特征

多数情态动词的用法上有如下特点：

1、它们后面总是跟动词原形。

2、其形式不受主语的单复数和人称的影响。

3、多数情态动词只有一般式和过去式两种形式变化。

（三）常见情态动词

英语中常见常用的情态动词如下表所示：

情态 动词	用法	例句（表现在或将来）	例句（表过去）
can / could	表能力、许可、请求或可能性。	I can learn modal verbs online. You can use my car tomorrow. Can I borrow your book? Cats can't swim.	I could jump high a few years ago but now I can't. That can't have been true!
have to	表必要性。	I have to go to class today. I don't have to go to class today.	I had to go to class yesterday. I didn't have to go to class yesterday.
have got to	表必要性。	I have got to go to class today	I had to go to class yesterday.
had better	表强烈建议。	You had better be on time.
may	表许可、请求或委婉可能性。	May I borrow your book? You may leave the room. He may be at the school.	He may have been at school.
might	表委婉可能性。	He might be at school.	He might have been at school.
must	表强烈的必要性、强制禁令或较大的可能性。	I must go to class today. You must not open that door. Mary isn't in class. She must be sick.(present only)	I had to go to class yesterday. Mary must have been sick yesterday.
ought to	表强烈建议或较大可能性。	I ought to study tonight. She ought to be at school	I ought to have studied last night. She ought to have done well on the test.
shall	用于第一人称表请求。	Shall I invite them too? Shall we dance?
should	表强烈建议或较大可能性。	I should study tonight He should be at school	You should have paid your bills. He should have done well on the test.

（四）更多情态动词

情态 动词	用法	例句（表现在或将来）	例句（表过去）
be supposed to	表预期。	We are supposed to meet them here.	We were supposed to meet here.
be to	表强烈预期。	We are to meet them here.	We were to meet them here.
would like (to)	表想法。	I would like to learn English free.
would rather	表偏好。	I would rather walk than drive.
need	常用于否定，表不必。	She needn't go there alone. He needn't have done it.

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