May I traditionally asks for permission, and can I traditionally asks about ability. That is the basic grammar rule many learners study first.
For example:
- May I leave early?
- Can you swim?
In real everyday English, however, can I is also very common for asking permission. Many native speakers say Can I leave early? in casual situations, and it sounds natural.
A simple way to choose is this:
- Use may when you want a more formal, careful, or polite tone.
- Use can for ability, and also for permission in everyday conversation.
So both forms can ask for permission, but they do not always sound the same. May I ask a question? sounds more formal. Can I ask a question? sounds more relaxed and conversational.
If you are unsure, remember this quick guide: may is safest for formal permission, and can is normal in everyday speech.
