允许；可以

You can stay with us. 你可以留下来跟我们一起。

You can't smoke in the room. 你不可以在室内吸烟。

You can/can't park your car in front of my house.

你(不)可以把车停在我家前面。

Can I talk to you in private? 我可以私下跟你谈一谈吗？

推测 (后面常接be)

Can the news be true? 那消息会是真的吗？

No, it can't be true. 不可能是真的。

May I have some sandwiches? 我可以吃点三明治吗？

You can't be hungry. You've just had your breakfast.

你不可能饿的，你才刚吃过早餐。

How can he be so cruel to dogs? 他怎么会对狗那么残忍？