Short answer
‘Can’ commonly expresses ability and is also standard for everyday permission. ‘May’ expresses permission, often with a more formal tone, and can also express possibility. The familiar schoolroom rule that permission always requires ‘may’ is stricter than actual US English usage. 1 2 3
Both are modal verbs with overlapping uses for permission and possibility, but ‘can’ is more informal and typical for ability, while ‘may’ is more formal for permission.
On this page
At a glance
Scroll to compare all columns →
| Question | can | may |
|---|---|---|
| Core use | Ability; also permission | Permission or possibility |
| Permission tone | Everyday and standard | Often more formal |
The table summarizes the stated definitions and scope. 1 2 3
What each thing is
Can. In contemporary US English, ‘can’ is a modal verb used to express physical or mental ability, possibility, or, informally, to request or grant permission. 1 2
May. ‘May’ is a modal verb primarily used to indicate permission or possibility, and is generally considered more formal than ‘can’ when granting or requesting permission. 1 3
Key differences
The main distinction is that ‘can’ is the default for expressing ability, while ‘may’ is traditionally used for formal permission. Both can indicate permission, but register and context influence the choice. 1 2 3
How to tell them apart
To test which to use, consider if you are emphasizing ability or seeking/giving permission. For formal requests, ‘may’ is safest. In everyday speech, ‘can’ is widely accepted for both. 1
Where they overlap
Both ‘can’ and ‘may’ are used to grant or request permission and to express possibility. In these senses, they are often interchangeable, especially in spoken or informal contexts. 1 2 3
Edge cases
Negative forms show why context matters: ‘You may not leave’ can express a prohibition, while ‘It may not rain’ expresses uncertainty. ‘Can not’ or ‘cannot’ can also concern ability or permission. These possibilities depend on the sentence, not on a blanket rule about one verb. 2 3
Why the distinction exists
The difference is rooted in their linguistic roles: ‘can’ evolved to express ability and later permission, while ‘may’ has a longer history of granting permission. Today, usage is shaped more by formality than strict rules. 1
Common misconceptions
A common misconception is that ‘can’ must only express ability and ‘may’ only permission. In reality, both are used for permission, with ‘can’ being informal and ‘may’ more formal. 1
Examples
Compare: ‘Can I leave early today?’ (informal request for permission) and ‘May I leave early today?’ (formal request). Both ask for permission, but the second is more formal in tone. 1 3
Sources
Sources checked October 3, 2026.
- Merriam-Webster — Can vs. May: How to Use Them. Usage guide: definitions, examples and exceptions.
- Merriam-Webster — Can Definition & Meaning. Dictionary entry: definitions, usage examples and word history.
- Merriam-Webster — May Definition & Meaning. Dictionary entry: definitions, usage examples and word history.