Every day you need to say what you are able to do and to ask if something is okay. At work you ask, 'Can I take Friday off?' In a shop you ask, 'Could I try this on?' On a trip you check, 'Are we allowed to take photos here?' These small questions open doors. If you cannot form them, you stay silent, or you sound like you are giving orders instead of asking.

This grammar also protects you from sounding rude by accident. 'Give me the menu' and 'Could I see the menu?' ask for the same thing, but they feel very different to the listener. Learning can, could, may, and be allowed to gives you polite, natural ways to talk about ability and permission.

Can, could, and may are modal verbs. A modal verb is a small helper verb that adds a meaning like ability or permission to the main verb. The form rule is simple and very strict: after a modal, use the base verb with no 'to' and no ending. Say 'I can drive', never 'I can to drive' or 'I can drives'. Modals also never change: it is 'she can', not 'she cans'.

For ability now, use can: 'I can cook', 'She can speak French'. For ability in the past, use could: 'I could run fast when I was a child'. To make a question, move the modal before the subject: 'Can you swim?' To make a negative, add not: 'I cannot (can't) swim', 'He couldn't come yesterday'. You never need 'do' with a modal, so 'Do you can swim?' is wrong.

For permission, English gives you a scale of politeness. 'Can I sit here?' is friendly and normal. 'Could I sit here?' is softer and more polite, good with strangers or at work. 'May I sit here?' is the most formal; you hear it in offices, schools, and polite service. All three use the same pattern: modal + subject + base verb.

Be allowed to is not a modal, but it works as a partner. Use it to talk about rules made by other people: 'Visitors are not allowed to smoke here', 'Are we allowed to park outside?' It is very useful where modals cannot go. Modals have no past or future forms for permission, so we say 'We were allowed to leave early' and 'You will be allowed to enter at nine'. Notice that be allowed to changes with the subject and tense (am, is, are, was, were), because it is a normal verb phrase, not a modal.

So choose like this: can for everyday ability and casual permission, could for past ability and polite requests, may for formal permission, and be allowed to for official rules and for past or future permission.

1. 1. Can you drive a truck?

   Question about ability: modal 'can' moves before the subject, and 'drive' stays in base form.

2. 2. I can't open this jar; my hands are wet.

   Negative ability now: 'can't' plus the base verb 'open'.

3. 3. My grandmother could sew beautiful dresses.

   'Could' shows a general ability in the past.

4. 4. Could you help me carry these bags?

   'Could you' makes a polite request to another person.

5. 5. May I use your phone for a minute?

   'May I' is the most formal way to ask for permission.

6. 6. Can I pay by card here?

   Casual permission question in a shop; note the base verb 'pay'.

7. 7. You can leave your coat on that chair.

   'Can' also gives permission, not only ability.

8. 8. Staff are allowed to park behind the building.

   'Be allowed to' describes an official rule at work.

9. 9. We weren't allowed to take photos in the museum.

   Past permission needs 'were allowed to', because modals have no past permission form.

10. 10. Could I open the window? It's hot in here.

    'Could I' asks for permission more softly than 'Can I'.

11. 11. She can speak three languages, but she can't write them.

    One sentence contrasts positive and negative ability.

12. 12. Passengers may board the plane from gate six.

    Formal 'may' gives official permission in announcements.

13. 13. I couldn't hear you; the music was too loud.

    'Couldn't' shows something was not possible at a past moment.

14. 14. Will we be allowed to check in early?

    For future permission, use 'will be allowed to', not a modal.

The biggest mistake is adding 'to' after a modal. Learners say 'I can to leave early' because many verbs do take 'to' ('I want to leave', 'I need to leave'). But modals are different: they take the bare base verb. Wrong: 'I can to leave early.' Right: 'I can leave early.' If you remember one rule from this lesson, remember this one: modal + base verb, nothing in between.

A second mistake is changing the modal or the main verb for he, she, or it: 'She cans swim' or 'He can swims'. Modals never take -s, and the verb after them never does either. Wrong: 'He can cooks well.' Right: 'He can cook well.' The modal carries the grammar; the main verb stays plain.

A third mistake is using 'do' in questions and negatives: 'Do you can drive?' Modals make their own questions and negatives. Wrong: 'Do you can drive?' Right: 'Can you drive?' Wrong: 'I don't can come.' Right: 'I can't come.' Also be careful with past permission: say 'We were allowed to leave', not 'We could to leave'.

• After can, could, and may, always use the base verb: can go, could see, may enter.
• Never put 'to' after a modal: 'can leave', not 'can to leave'.
• Politeness scale for asking: Can I (friendly), Could I (polite), May I (formal).
• Use could for past ability: 'I could ski when I was ten.'
• Use be allowed to for rules and for past or future permission.
• Modals never take -s and never use 'do' in questions or negatives.