情态动词学习笔记(4) 基本用法：许可(can、may、be a

can 用于口头语

may 多用于书面正式语

can/may = be allowed to

例句：

you can use my car tomorrow
you are allowed to use my car tomorrow

you can leave now ,he may not leave.

否定句：

can not /may not

must not也可表示拒绝许可，但语气更强烈。

could/might 用来表示过去的许可

could/might/was allowed to 能表示过去一般的许可
要表达具体场合的某一个活动只能用was/were allowed to不能用could/might
例句：
they might have a break after lunch 那时，他们吃完午饭后是可以休息一会儿的

they were allowed to have a break after lunch 那次，他们吃完午饭后被允许休息了一会儿