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Modal Verbs Can and Could
'Can' and 'could' are both modal verbs that are mainly used to express ability, possibility, permission, and requests. 'Could' is used to express past ability, possibility, or permission. It can also be used to make polite requests.
Can and Could: Functions
'Can' and 'could' are used to:
Talking about Ability
One of the most common uses of the modals 'can' and 'could' is talking about abilities.
Can
Can is used to talk about abilities that someone has in the present or future, based on their knowledge or talent. For example:
I can drive.
She can sing really well.
Could
Could is used to talk about general abilities in the past. We use it to talk about what someone was able to do in the past.
My uncle could speak five languages.
Use of 'could' indicates that maybe his uncle can no longer speak five languages, or maybe he is dead.
By the time he was seven, he could read and write.
Be Able to Vs. Can
While 'can' and 'could' are commonly used to talk about abilities, they may not be appropriate in every situation. Sometimes it is more appropriate to use alternative expressions such as 'be able to'.
'Can' and 'be able to' generally have the same meaning when used to talk about abilities and in most situations, either one can be used. However, 'be able to' is considered more formal than 'can', and may be more appropriate in formal or professional contexts.
I can play the piano. = I am able to play the piano.
I could jump very high when I was younger. = I was able to jump very high when I was younger.
Additionally, 'can' and 'could' cannot be used with every verb tense and form. When using perfect tenses or gerunds to talk about abilities, it is more appropriate to use 'be able to.'
I have been able to dance since I was three years old.
Here, we cannot use 'can' or 'could' and still convey the same meaning.
I like being able to watch my favorite TV shows on YouTube.
With verbs such as 'like' we need a gerund after them. So we cannot use 'can' or 'could' in this situations.
On the other hand, 'can' and 'could' are used with verbs such as see, hear, understand, notice, etc. while 'be able to' is not typically used with these verbs.
I can hear a noise.
Do not say "I am able to hear a noise."
I could understand every word he said.
Do not say "I was able to understand every word he said."
Be able to or Could?
Both 'could' and 'be able to' can be used to talk about abilities in the past. But they are not always interchangeable.
For example, if you want to talk about a specific ability or achievement you must use 'be able to' and using 'could' would be incorrect. Pay attention to the examples:
I was able to pass the driving test on the first try.
In this example, we are talking about a specific achievement in the past and we cannot use 'could' in this example.
I was able to reserve a table, although it was very busy.
In this example we are talking about an achievement so we cannot use 'could.'
You can use 'managed to' to talk about specific abilities in the past.
I managed to reserve a table, although it was very busy.
Specific or General Abilities in Affirmatives
You only need to focus on the difference between specific and general abilities in affirmative sentences. There's no need to distinguish between them in negative sentences.
I couldn't reserve a table.
No need to use 'to be able to' in a negative sentence.
I couldn't pass the driving test on the first try.
Two modal verbs cannot be used in one sentence at the same time, i.e. you cannot use 'can' or 'could' with other modals like 'should' or 'would.' In such cases, 'be able to' is used instead of can/could.
You should be able to choose your own religion. (Not You should can choose ...)
I would be able to give you an appointment for January 3rd. (Not I would can give you ...)
Could: Hypothetical or Real?
'Could' can have two different meanings:
Could = was/were able to (abilities in the past)
Could = would be able to (hypothetical ability in the future)
I could understand what he meant by that. = I was able to understand what he meant by that.
If you called me, I could help you. = If you called me, I would be able to help you.
Talking about Possibility
'Can' is commonly used to talk about something that is possible in the present or future, while 'could' is commonly used to talk about possibilities in the past.
Can you come back tomorrow?
Here, the sentence means 'Is it possible for you to come back tomorrow.' So, can does not show an 'ability,' but it shows a 'possibility.'
The auditorium can be emptied in five minutes.
Could: Hypothetical or Real?
'Could' can have two different meaning:
possibilities in the past
hypothetical possibilities in the past
I couldn't have left it on the bus.
I could have done it, if you had asked.
Could have is used when you are saying that it was possible for somebody to do something in the past but they did not try.
Making a Request
'Can' is also used to make a request. But keep in mind that this use of 'can' is very informal.
Can I borrow your book?
Can you help me with my homework?
Making a Polite Request
'Could' is not necessarily used in the past tense. It is also used in the present tense to make a polite request.
Could I have a glass of water, please?
Here, the request is being made politely at the present time.
Asking for or Giving Permission
'Can' is also frequently used to ask for permission to do something or to give somebody permission to do something.
You can take the car, if you want.
In this sentence the person is giving permission.
Can we wear jeans at work?
'Could' is used to ask for permission to do something politely.
Could I use your phone?
Could I leave?
Can't or Cannot?
The words 'can' and 'not' can be combined into one word, 'cannot', which is more formal and commonly used in written English. In informal English, it is more common to use the contraction 'can't' instead of 'cannot.'
He cannot believe what she's saying right now.
Review
Can is used a lot in daily English and even in formal writings. It has many functions. Now, look at the table.
To give or ask for permission | Can I put my cloth on your bed? |
|---|---|
to talk about abilities | She can speak Spanish. |
To request something informally | Can you order us pizza. |
To talk about possibilities | Take your umbrella with yourself! It can be rainy outside. |
Could is the past tense of 'can,' but it is not always talking about the past. Look at the chart below:
To talk about past abilities | I could swim back then. |
|---|---|
To make a polite request | Could you please close the window? |
To talk about possibilities in past | Even now, I cannot believe us. It could be dangerous to be there. |
To talk about hypothetical possibilities | I could have been a Doctor by now if I studied more. |
When it comes to expressing your ability, you can not always talk in present simple and past simple tenses, So, there must be an alternative for them in other tenses such as present perfect. In this case, you use be able to.
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