Can / Can't

1. Overview & Concept

• What is it? Can and can't (cannot) are modal verbs used to express ability, possibility, and permission in the present or general time.
• Purpose: We use can to say that someone is able to do something, that something is possible, or that something is allowed. We use can't (the negative form) to say the opposite — inability, impossibility, or prohibition.

2. Structure & Formula

Affirmative:

Subject + can + base verb

Negative:

Subject + can't / cannot + base verb

Question:

Can + subject + base verb?

Short answers:
- Yes, I can. / No, I can't.

Key grammar rules for can:
- Can never changes form — no -s, -ed, or -ing.
- Always followed by a bare infinitive (base verb, no to).
- Cannot is the full form; can't is the contracted spoken form. Both are correct.

3. Usage Rules

• Rule 1 — Ability (present): Use can to describe a skill or physical/mental ability someone possesses right now.
• She can play the piano beautifully.

• I can't ride a bicycle.

• Rule 2 — General possibility: Use can to say that something is generally or theoretically possible.

• Accidents can happen anywhere.

• You can get good deals online.

• Rule 3 — Permission (informal): Use can in informal contexts to ask for or give permission.

• Can I use your phone? (asking permission)
• You can sit here. (giving permission)

• You can't park here. (refusing permission)

• Rule 4 — Requests: Use can to make an informal request.

• Can you open the window, please?

• Rule 5 — Offers: Use can to offer help.

• I can carry that bag for you.

Comparison table — Can vs. May (permission):

4. Signal Words & Context Clues

• Ability context: words like well, fluently, easily, quickly — She can speak French fluently.
• Permission context: phrases like Is it OK if…, Is it all right to… — the answer often uses can/can't.
• Possibility context: words like sometimes, often, generally, theoretically.
• Request context: please at the end of a question — Can you help me, please?

5. Common Pitfalls & Mistakes

• ❌ She cans swim. → ✅ She can swim. (Modal verbs never take -s in third person.)
• ❌ He can to drive. → ✅ He can drive. (Never use to after a modal verb.)
• ❌ Can you speaking English? → ✅ Can you speak English? (Use bare infinitive, not -ing.)
• ❌ I cannot to go. → ✅ I cannot go. (Even with cannot, no to.)
• ❌ She can swims. → ✅ She can swim. (Base form only; no -s.)

6. Real-World Examples

1. I can speak three languages: English, Spanish, and French.
2. My little sister can't swim yet, but she's learning.
3. Can you hear that noise outside?
4. You can't use your phone during the exam.
5. This app can translate text into over 50 languages.
6. Can I borrow your dictionary for a moment?
7. He can run 10 kilometres without stopping.
8. We can't find our keys anywhere.
9. Can the doctor see me today?
10. Stress can cause serious health problems.

7. Summary Table