一、can/could与be able to
1．can/could用来表示“一般能力”；be able to有多种时态，且用来表示在特定条件下的“具体能力”。如：
My grandma is over seventy，but she can still read without glasses.
They will be able to tell you the news soon.
He was able to flee Europe before the war broke out.
2．表示允许可用can或could，与may/might意义接近。could可用于现在时，只是语气更加委婉、客气，回答时则一般要用can而不用could。
—Could I have the television on?
—Yes，you can./No，you can't.
二、may与might
1．表示允许，意为“可以，许可”，用法基本上同can与could。如：
