Can is the most common modal we use to talk about ability in the present and future:
I can give you a lift this evening if you like.
Can you pick up spiders?
Can or be able to?
We sometimes use be able to with the same meaning as can:
I can't / am not able to give you an answer at the moment.
We use modals like will with be able to as a future form of can:
One day people will be able to go for a holiday on the moon. I might be able to help you.
We also use be able to in the infinitive and ing form. We sometimes use verbs likened and seem instead of be:
I'd like to be able to write as well as that. I like being able to do exactly what I please. I don't seem able to find the energy for playing football these days.
We commonly use can, not be able to, with the meaning 'know how to', and with verbs related to the senses like see, hear.
Can you read music? I can smell something burning.
Could, and sometimes would be able to, are common in conditional sentences, referring to the present or future. Could is more tentative than can:
I could come a bit earlier if that would be helpful.
We use could, or sometimes was able to after wish to talk about hypothetical ability:
I wish I could cook.
Theoretical possibility
Rather than expressing ability, we sometimes use can to say that something is possible in theory: Speaking in public can be quite traumatic for many people. It can still be very hot in Egypt in September.
Ability in the Past Could
We often use could as a past form of can: I could hear a noise and went outside.
Could (have) or was able to?
For general ability in the past, we use could or was able to. Could is more common:
I could/was able to swim when I was five years old.
For a specific event showing success after trying, we use was I were able to, managed to or succeeded in, but not could:
I was able to/ managed to solve her problems for her.
We can use could or would have been able to to talk about conditional or hypothetical past ability:
I wouldn't have been able to find her in that crowd even if I'd known she was there. He could have helped me, if he'd tried. (= but he didn't) He couldn't have helped me anyway. (= he didn't)
Permission
We use can and could as well as other modals to give and ask for permission:
Can I go now? No, you can't. I won't let you. They asked if they could go.
Politeness and formality
When giving or asking for permission, or making requests or offers, the degree of politeness or formality depends strongly on the situation, stress and intonation, and who is speaking to whom. As an approximate guide, may and might are more polite and formal; could and would are more polite than can and will:
Can I leave early today? Of course you may.
Could I possibly use your phone?
Visitors to the college may not enter private rooms.
We often use might with wonder:
I wonder if I might have your attention for a moment.
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However, because may and might are formal, they can sound aggressive or sarcastic:
Might I suggest that you talk to the manager about it? And where have you been, may I ask?
Ex.4. Rewrite each of the following sentences using a modal. More than one modal may be possible:
Example: Is there any chance of me borrowing your Walkman tomorrow afternoon?
Can /Could /May I borrow your Walkman tomorrow afternoon?
1 Is it all right if I miss the first few minutes of tomorrow's meeting?
2 I wish my writing in English was better.
3 One day soon, Internet access is sure to be available to every schoolchild.
4 I knew how to swim before I was three.
5 A wasp sting was sometimes a cause of death in those days.
6 These photocopiers have proved to be quite temperamental.
7 The journey here took us twice as long as it needed to.
8 Even if they'd wanted to land at Heathrow, it was impossible because of the fog.
9 And what is this baby doing sitting on my desk, if you don't mind my asking?
Ex.5. Fill each of the gaps with a form of be able to followed by an appropriate verb:
Example: I don't think I will be able to drive you to the airport.
1 Inever...... out the difference between a PC and a Mac.
2 I would really love myself more interestingly on paper.
3 You him on this number, but I have my doubts.
4 They........... just the drowning man to safety, thank
goodness.
5................... If you don't feel a contribution, just say so.
Ex.6. The outgoing President is in bullish mood. Complete his claims with could, could have, or a suitable form of be able to plus an appropriate verb:
Example: No one could have done more than I have to increase this country's standing in the world.
1.............................. In my first term of office I. this country back on its feet after my predecessor's mistakes.
2........................ In this second term I in the most exciting new legislation this country's seen for decades.
3 With anyone else in power, there economic chaos.
4 I my head up high throughout my presidency.
5. I any allegations you care to make against me.
6. I new measures which will eventually make the world a far better place.
Ex.7. Complete the second sentence so that it has a similar meaning to the first sentence, using the word given. Do not change the word given. You must use between three and eight words, including the word given:
1 I hope one day we can agree more favourable terms.
reach
I hope one day it on more favourable terms.
2 Some supermarket beef can be rather tough.
Tendency
Some supermarket beef rather tough.
3 Would you kindly inform everyone of the change of
procedures?
Wonder
I... as to inform everyone of the change of procedures?
4 Maybe I could have helped you.
possible
Maybe help you.
5 In the end we were able to communicate with sign language.
message
In the end we succeeded across with sign language.
