Can, Could, and Be Able To
Can, could, and be able to are fundamental modal verbs that express ability, possibility, permission, and requests in English. These versatile modals form the foundation of polite communication and practical expression, allowing you to discuss what people can do, what might be possible, and how to ask for things courteously.
Understanding the subtle differences between these three forms is essential for natural English communication. Can is the most common and informal, could adds politeness and past ability, whilst be able to provides flexibility across all tenses and formality levels. Each has specific contexts where it works best.
These modals are amongst the first that English learners encounter, but their full range of uses extends far beyond basic ability. They express varying degrees of politeness in requests, different levels of certainty about possibilities, and nuanced distinctions between what someone is capable of doing versus what they are permitted to do.
Mastering can, could, and be able to will give you the tools to express yourself politely and effectively in both casual and formal situations. These modals are essential for making requests, discussing abilities, exploring possibilities, and navigating the complex social dynamics of English-speaking environments with confidence and appropriateness.
Formation
Can
Subject + can + base verb
Present ability, possibility, and informal permission/requests
Positive:
- I can swim very well.
- She can speak French fluently.
- We can help you tomorrow.
- They can come to the party.
Negative:
- I can't drive yet.
- She cannot attend the meeting.
- We can't afford that holiday.
- They can't solve this problem.
Questions:
- Can you help me?
- Can she come with us?
- Can we leave early?
- Can they understand English?
Could
Subject + could + base verb
Past ability, polite requests, suggestions, and weak possibility
Past ability:
- I could swim when I was five.
- She could speak German before.
- We couldn't afford it then.
- They could see the mountain clearly.
Polite requests:
- Could you help me, please?
- Could I borrow your pen?
- Could we meet tomorrow?
- Could you speak more slowly?
Suggestions:
- We could go to the cinema.
- You could try calling her.
- They could take the train instead.
- She could ask for help.
Be Able To
Subject + be (am/is/are/was/were/will be) + able to + base verb
Ability in all tenses, formal contexts, and after other modals
Present:
- I am able to work late tonight.
- She is able to speak five languages.
- We aren't able to attend.
- They are able to help us.
Future:
- I will be able to drive next year.
- She won't be able to come.
- We will be able to finish tomorrow.
- Will you be able to help?
Perfect forms:
- I have been able to improve.
- She had been able to work.
- We might be able to come.
- They should be able to help.
Common Mistakes to Avoid
❌ "I can to speak English."
✅ "I can speak English."
Don't use 'to' after modal verbs - they're followed by the base form
❌ "She cans play piano very well."
✅ "She can play piano very well."
Modal verbs don't change form - no 's' for third person singular
❌ "I will can help you tomorrow."
✅ "I will be able to help you tomorrow."
Use 'be able to' after other modal verbs, not 'can'
❌ "Could you to explain this?"
✅ "Could you explain this?"
Don't add 'to' after 'could' in questions
❌ "I have can swim since childhood."
✅ "I have been able to swim since childhood."
Use 'been able to' in perfect tenses, not 'can'
Politeness Levels in Requests
Casual (friends/family):
- Can you help me?
- Can I borrow this?
- Can we go now?
Polite (colleagues/acquaintances):
- Could you help me, please?
- Could I possibly borrow this?
- Could we leave a bit early?
Very polite (formal situations):
- Would you be able to help me?
- I wonder if I could borrow this?
- Would it be possible to leave early?
Could vs Was/Were Able To (Past)
Could (general ability):
- When I was young, I could run very fast. (had the ability)
- She could speak French when she lived in Paris. (general skill)
- We couldn't afford holidays then. (general situation)
Was/were able to (specific achievement):
- Yesterday I was able to run 10km. (successful specific action)
- She was able to translate the document. (accomplished the task)
- We were able to buy a house last year. (achieved the goal)
Expressing Future Ability
Will be able to (definite future ability):
"After the course, I will be able to use advanced Excel functions."
Might be able to (possible future ability):
"I might be able to come to the party if I finish work early."
Should be able to (expected future ability):
"The new system should be able to handle more users."
Quick Reference Guide
Key Points:
- Can: Present ability, informal requests, general possibility
- Could: Past ability, polite requests, suggestions, weak possibility
- Be able to: All tenses, formal contexts, after other modals
- Politeness: Could is more polite than can for requests
- Future: Only 'be able to' works for future ability
- Perfect tenses: Use 'been able to', never 'can' or 'could'
- After modals: Must be able to, should be able to, might be able to
- Formal writing: Prefer 'be able to' over 'can' in professional contexts
- Past achievement: 'Was able to' often better than 'could' for specific successes