Simple rules to learn how to use "may" and "can" to talk about permission, ability or possibility.

Before using the words can or may in English, you should consider what you are about to say:

• a permission or request,
• an ability (something you know how to do), or
• a possibility.

1. Permission or Request

Asking for Permission

In this case we use can, could or may, but their level of formality is different:

• Can (informal and acceptable in most situations)
• Could (formal)
• May (the most formal)

Examples (asking for permission)

• Can I go to the bathroom?
• Can I have a beer?
• Could you please go to the supermarket for me?
• Could you go to the site and fill out the form?
• May I come in?
• May I visit your mother?

Giving Permission

We use can or may to give permission:

• Can. We normally use this verb to give permission.
• May. It's less common.
• Could. We never use the verb could to give permission.

Examples (giving permission)

• Yes, you can.
• Yes, you can go to the bathroom.
• Peter, you may call me tomorrow.

Denying Permission

We use may not or cannot (can't) to deny a permission.

Examples (denying permission)

• You may not use the computer during the exam.
• You can't drive my car tonight.
• Peter, you cannot draw with my pen.

2. Ability

You can talk about your physical or mental abilities by using the verb can, for example, to say that you are able of doing something or know how to do something.

Examples (ability)

• I can swim.
• My sister can play basketball.
• I can speak French and English.
• My cousin can play the guitar.

3. Possibility

In this case we use may, can or could, but their meaning is slightly different:

• Can. We use can for a strong possibility or generally accepted truth.
• May/could. We use may or could for a weak possibility or uncertainty.

In other words:

• If you believe that the possibility is strong, use can.
• If you believe that there is a weaker possibility, use may or could.
• When you are certain that a fact is true, don't use any of them.

Examples (possibility)

• It can be dangerous to drive after drinking alcohol. The speaker believes that the risk of having an accident is high after drinking alcohol.
• The exam can be easy. The speaker thinks that the possibility of being easy is strong.
• History exams may be difficult. The speaker thinks that sometimes they are difficult.
• It may be dangerous to drive at night. The speaker thinks that this possibility is not very strong.