Can vs May: Ability vs Permission

Master the Difference Between Capability and Permission

Reviewed by the Grammarlyzer Editorial Team · Our Review Standards · Published January 22, 2026 · Updated June 13, 2026

📌 Quick Answer
Can expresses ability (what you are capable of doing). May expresses permission (what you are allowed to do). Use can for ability: "I can swim." Use may for permission: "May I leave?"

Memory Trick: CAN = Capability, MAY = perMission.

💡 The 90% Rule

Use can when asking "Am I able to?" Use may when asking "Am I allowed to?"

Quick Comparison

Form Use It For Quick Check
Can ability/capability, and informal permission Swap in am able to: I am able to swim fits.
May formal permission and specific possibility Swap in am allowed to or it is possible that.

Fast Decision Table

Pick the meaning you intend, then choose the modal. Register (formal vs casual) decides the gray areas.

What you mean Choose Example
Ability — able to do something can She can speak three languages.
Permission, formal/written may May I leave early today?
Permission, casual/spoken can (accepted) Can I grab a coffee?
Specific future possibility may / might It may rain tonight.
General possibility can Winters here can be harsh.

Common Mistakes

❌ Incorrect:

"Can I be excused from the meeting?" (in a formal context)

✓ Correct:

"May I be excused from the meeting?"

In formal settings, use may for permission requests. Can is fine in casual speech.
❌ Incorrect:

"May you swim?" (asking about ability)

✓ Correct:

"Can you swim?"

May is not used to ask about someone's abilities — that is always can.
❌ Incorrect:

"It can snow tomorrow."

✓ Correct:

"It may snow tomorrow."

For a specific future possibility, use may (or might). Can only fits general possibility: it can snow here in April.
❌ Incorrect:

"Guests cannot enter after 10 pm." (a posted rule)

✓ Correct:

"Guests may not enter after 10 pm."

To deny permission in a formal rule, use may not. Cannot literally states an inability, which is not the intended meaning of a policy.
❌ Incorrect:

"I think it can be a mistake."

✓ Correct:

"I think it may be a mistake."

Tentative possibility about one situation takes may or might, not can.

🎯 Test Your Knowledge

Choose the correct word.

1. "___ I leave early today?" (formal office setting)

2. "She ___ speak three languages fluently."

3. "It ___ snow tomorrow." (specific possibility)

4. "Visitors ___ not park in reserved spaces." (a posted rule)

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The correct version is: "May I be excused from the meeting?".

Honest limits: this is a meaning problem, not a spelling one. Since Can and May are real words, the engine may wave a wrong choice through (Ability vs Permission); confirm the sense against the rule on this page.

Frequently Asked Questions

What is the difference between can and may?

Can expresses ability or capability ("I can swim"). May expresses permission or possibility ("May I leave?" or "It may rain"). In formal contexts, use "may" for permission.

Is "Can I go to the bathroom?" correct?

While commonly used, "Can I go?" technically asks about ability. Formally, "May I go?" is correct for permission. However, "can" is widely accepted in casual speech.

When should I use may instead of can?

Use "may" in formal situations when asking for permission (May I speak?), expressing possibility (It may rain), or in polite requests. Use "can" for ability and informal permission.

What is the difference between may and might?

Both express possibility, but might suggests a slightly smaller or more hypothetical chance. It may rain sounds more likely than it might rain. Might is also the past form of may in reported speech: she said she might come.

Can "can" express possibility?

Yes, but a general one. Can describes things that are generally possible (accidents can happen). For a specific future possibility, use may or might (it may snow tonight), not can.

Is it "may not" or "cannot" to refuse permission?

To deny permission formally, use may not: guests may not enter after 10 pm. Cannot refers to ability or impossibility: he cannot swim. In speech, can't is common, but may not is the precise formal choice.

Is "can" acceptable in formal writing for permission?

It is increasingly accepted, but may remains the safer, more traditional choice in formal documents, policies, and academic writing. When in doubt in a formal context, use may for permission.

When to Use "Can"

Professional Examples

  • "Our team can complete the project by Friday." (ability)
  • "The software can process 10,000 transactions per second." (capability)

Academic Examples

  • "Students can access the library database remotely." (ability)
  • "This theory can explain the observed phenomena." (capability)

Casual Examples

  • "I can meet you after work." (ability)
  • "She can run a marathon." (physical capability)

When to Use "May"

Professional Examples

  • "May I schedule a meeting with you?" (formal permission)
  • "Employees may take breaks every two hours." (allowed)

Academic Examples

  • "Students may use calculators during the exam." (permission)
  • "The results may vary depending on conditions." (possibility)

Casual Examples

  • "May I have another cookie?" (polite request)
  • "It may rain later." (possibility)

Word Origins & Etymology

Can comes from Old English 'cunnan' (to know, to know how to). Its original meaning was 'to know how' — ability. Using 'can' for permission is a later development that purists resist.

May derives from Old English 'magan' (to be able, to have power). Paradoxically, 'may' originally meant ability (like 'can' today), but shifted to permission over centuries.

🔗 The Connection

Historically, 'may' expressed ability and 'can' expressed knowledge. Their meanings almost completely swapped over centuries. The 'Can I go?' vs 'May I go?' debate is a remnant of this swap.

Real-World Examples

📏 Ability:

She can run a mile in under six minutes.

Can = ability (she has the physical capacity)
📏 Permission:

May I borrow your pen?

May = formal permission request
🗣️ Daily:

Can you pass the salt?

Can for requests is universally accepted in modern English
🏫 Classic:

Student: 'Can I go to the bathroom?' Teacher: 'I don't know, can you?'

The classic teacher joke enforces the can=ability, may=permission distinction
💼 Business:

May I suggest an alternative approach?

May = polite/formal permission
🔮 Possibility:

It may rain later, so bring an umbrella.

May = possibility (it's possible that)
❌ Debatable:

Can I have a glass of water?

Prescriptivists say 'may I' is correct for permission. But 'can I' is universally understood and accepted in all but the most formal contexts.
💡 Modern View:

In modern English, can is used for both ability AND permission in all but the most formal settings. May is reserved for formal permission and possibility.

The strict distinction is fading; formality is the deciding factor

Why Do People Confuse Them?

The can/may distinction is slowly dying in everyday English. 'Can I?' is universally understood as a permission request, regardless of prescriptive rules. The distinction matters only in very formal writing or when clarity between ability and permission is essential. Many linguists consider enforcing this rule a form of prescriptive snobbery.

Practice with Related Guides

Keep practicing with closely related guides: Could vs Would vs Should and Modal Verbs Guide.

Related Articles

Can vs May in Legal, Policy, and Official Writing

In formal documents where precision has legal or contractual implications, the can/may distinction matters more than in everyday speech. Using the wrong modal in a policy, contract, or official rule can create genuine ambiguity about whether a provision describes an ability or grants permission.

In contract and legal language

May is the standard modal for granting or withholding permission in contracts and legal documents: "Either party may terminate this agreement with 30 days' written notice." "The licensee may not sublicense the software without written consent." Using can in these contexts introduces ambiguity — does "the licensee can terminate" mean they have the legal right, or merely that they are technically capable of doing so? Legal drafters choose may to remove that ambiguity.

In company policies and handbooks

May signals what is allowed: "Employees may request flexible scheduling with manager approval." Can signals technical capability: "Employees can access the VPN from any device." When writing policies, use may for permissions and prohibitions, and reserve can for descriptions of technical ability or system function. This distinction helps readers immediately understand whether they are reading a permission or a capability description.

In academic writing

Academic style has largely abandoned the strict prescriptive distinction for general prose but preserves it for specific uses. May is preferred for expressing hedged possibility in scholarly writing: "These results may indicate a causal relationship." This is more tentative than "can indicate," which sounds more assertive. For methodology sections describing what the study permits participants to do, may is the precise choice: "Participants may withdraw from the study at any point without penalty."

In everyday professional writing

In most professional emails, reports, and presentations, the strict can/may distinction has low stakes. Using can for informal permission requests ("Can I get your thoughts on this?") is standard and appropriate. Reserve the shift to may for formal requests in contexts where politeness or hierarchy matters: "May I request an extension on the submission deadline?" The degree of formality the situation requires is the practical guide.

The Full Modal Landscape: Can, May, Might, and Could

Understanding can and may is easier when you see them alongside the other related modals. Each one occupies a slightly different position on the ability-permission-possibility spectrum.

Modal Primary Use Example Formality
Can Ability; informal permission; general possibility She can speak French. Can I help you? Neutral to informal
May Formal permission; specific possibility (more likely) May I leave? It may rain. Formal
Might Tentative possibility (less likely than may); past of may It might work. She said she might come. Neutral
Could Past ability; polite request; conditional possibility Could you help me? I could try that. Neutral to formal

For the full treatment of how these modals interact, see the modal verbs guide and the could vs would vs should guide.

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