Try this quick quiz. In which of the questions below can you substitute ‘can/could’ with ‘be able to’ and vice versa? And can you explain why?
1) How many languages can you speak?
2) Do you think you will be able to understand this grammar point?
3) Have you been able to study OK recently?
4) Do you think it’s important to be able to speak a foreign language perfectly?
5) Could you do anything when you were younger that you can’t do now?
In this lesson we’ll look at when we use ‘can’ and when ‘be able to’ is required when talking about ‘ability’.
Uses
‘Can’, ‘could’ and ‘be able to’ are all used to describe ability but there are important differences that you should be aware of.
a) Can is preferred if we are talking about a general ability:
Can you speak French?
I can play the piano quite well.
b) ‘Be able to’ is normally used to refer to ability in the future:
I won’t be able to start university until next year.
Do you think you’ll be able to get a job when you leave college?
c) In positive sentences, ‘could’ and ‘be able to’ are used to talk about general ability in the past.
I could/was able to swim really well when I was younger. (generally)
However, if we are talking about the ability to do something on one particular occasion in the past, we use ‘be able to’. Many upper-intermediate and advanced level students get this rule wrong and use ‘could’. For example, this is incorrect:
The course was hard but I could pass the exam. (X)
This should be:
The course was hard but I was able to pass the exam. (particular occasion)
TIP: ‘Succeed in’ and ‘manage to’ are useful alternatives to ‘able to’ when we are talking about the ability to do something on one particular occasion:
I managed to pass the exam … (more common)
I succeeded in passing the exam …
d) In negative sentences, however, ‘couldn’t’/’wasn’t able to’ can be used to talk about inability to do something on a particular occasion:
I couldn’t/wasn’t able to understand my teacher in the first lesson but now it’s OK.
e) After modal or auxiliary verbs (be, do, have, should, etc) or ‘to+infinitive’ structures, ‘be able to’ is used:
I should be able to take a holiday this year.
I think it’s important to be able to do basic first aid.
So let’s look again at the question we posed at the beginning: in which of the questions below can you substitute ‘can/could’ with ‘be able to’ and vice versa? And can you explain why?
1) How many languages can you speak?
2) Do you think you will be able to understand this grammar point?
3) Have you been able to study OK recently?
4) Do you think it’s important to be able to speak a foreign language perfectly?
5) Could you do anything when you were younger that you can’t do now?
Can and ‘able to’ are possible in questions 1 and 5 as these are referring to general ability.
‘Able to’ is the only possible choice in 2 as it refers to the future.
‘Able to’ is the only possible choice in 3 because if follows an auxiliary verb.
‘Able to’ is the only possible choice in 4 because it follows a ‘to+infinitive’ structure.
Over to you
Practise the use of ‘can’ and ‘able to’. Describe a time when you succeeded in facing a challenge. For example:
I was never able to swim – it was always frustrating whenever I went on holiday and I wasn’t able to/couldn’t join my friends or family when they all went in the sea. So recently I decided to learn and was able to find a really good trainer at a local sports centre. I’ve taken several lessons now and the last time I went I was able to swim a length. Now, it’s great to be able to say ‘I can swim’!
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