Can and May
To express physical ability:
Incorrect : The patient may walk now.
Correct : The patient can walk now.
To express probability:
Incorrect : It can rain tonight.
Correct : It may rain tonight.
To seek permission politely :
Incorrect: Can I come in, Sir?
Correct : May I come in, Sir?
Note: "Can' is usually used to express physical ability or to seek permission informally but "may” is used to express probability or to seek permission politely and formally.
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