General possibility: "It can snow here in winter."
📝 Formation:
Affirmative: Subject + can + base verb
Negative: Subject + cannot/can't + base verb
Question: Can + subject + base verb?
⚠️ Important:
No 'to' after can: ✓ "I can swim" ✗ "I can to swim"
No -s for third person: ✓ "She can sing" ✗ "She cans sing"
2. COULD - Past Ability & Polite Requests
✅ When to use COULD:
Past general ability: "I could run fast when I was young."
Polite requests: "Could you please help me?"
Polite permission: "Could I borrow your pen?"
Possibility (less certain): "It could rain later."
📝 Formation:
Affirmative: Subject + could + base verb
Negative: Subject + couldn't/could not + base verb
Question: Could + subject + base verb?
⚠️ Important: Use 'could' for GENERAL past abilities. For a SPECIFIC achievement, use 'was/were able to'.
3. BE ABLE TO - Future & Special Situations
✅ When to use BE ABLE TO:
Future ability: "I will be able to travel next year."
After other modal verbs: "You might be able to solve it."
Perfect tenses: "I have been able to finish."
Specific past achievements: "I was able to pass the exam."
📝 Formation:
Present: am/is/are + able to + verb
Past: was/were + able to + verb
Future: will be + able to + verb
Present Perfect: have/has been + able to + verb
4. Quick Comparison Table
Situation
CAN
COULD
BE ABLE TO
Present ability
✅ I can swim.
❌
✅ I am able to swim.
Past general ability
❌
✅ I could run fast.
✅ I was able to run fast.
Past specific achievement
❌
❌
✅ I was able to escape.
Future ability
❌
❌
✅ I will be able to come.
Polite request
✅ Can you help?
✅ Could you help? (more polite)
❌
Permission
✅ You can leave.
✅ Could I leave? (polite)
❌
5. Common Mistakes to Avoid
❌ She can to swim. → ✅ She can swim.
❌ He cans speak English. → ✅ He can speak English.
❌ I didn't could come. → ✅ I couldn't come.
❌ I will can do it. → ✅ I will be able to do it.
❌ Could you helped me? → ✅ Could you help me?
❓ Frequently Asked Questions
Q1.What is the difference between 'can' and 'could' for requests?▼
'Can' is informal and direct: 'Can you help me?' 'Could' is more polite and formal: 'Could you please help me?' Both are correct.
Q2.Why can't we use 'can' for future?▼
'Can' has no future form. For future ability, use 'will be able to'. Example: 'I will be able to drive next year' (not 'I will can drive').