How to Choose Between Can, Could, and Be Able To in Sentences
An auxiliary verb is used with the main verb for helping in order to express the tense, mood, or voice of the main verb. ‘Can’ and ‘could’ are called modal auxiliary verbs. They are used to show the possibility or ability to do something in sentences. The use of ‘can and could’ differ in the tenses. ‘Be able to’ use the verb as the main verb and it is not an auxiliary verb. ‘Can’ and ‘could’, ‘be able to’ are used in a sentence for possibility and ability.
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Can
‘Can’ is an auxiliary verb also a kind of modal auxiliary verb. ‘Can’: is used to show about possibility and ability, make requests and ask for or give permission. This verb is used in only one form i.e. can hence it is invariable.
Structure of Can
The following is the basic structure for can that is used in sentences.
Subject + (can) auxiliary verb + main verb
Use of Can
The uses of ‘can’ can be better understood with the help of examples. The uses of ‘can’ are given below.
‘Can’ is used to show the possibility of something like what we are able or free to do. For examples:
She can cook dinner.
Ali can speak Urdu.
I cannot teach you.
Can you see me?
Generally, we use ‘can’ for the present. But it is also used when we make present decisions about future ability. For example:
Can you play badminton with me? (present)
I can help you tomorrow. (future)
‘Can’ is also used for requests and orders. When we use ‘can’ in a question to ask someone to do something. It is not a kind of real question because we do not really want to know if the person is able to do that work but we want them to do it. This way of using ‘can’ is informal. For example:
Can you stand up for a while, please?
Can you turn the alarm off?
Can you come here?
Can you keep quiet?
‘Can’ is also used to ask or give permission in a sentence. For example:
Can I eat this cookie?
You can have the seat.
Could
‘Could’ is also a modal auxiliary verb. It is used to talk about the possibility or ability of the past, to make requests. The main verbs in the sentences are always the bare infinitive. It is used in only one form that is, could, hence it is invariable.
Structure of Could
The following is the basic structure of could that is followed in sentences.
subject + (could) auxiliary verb + main verb
We can understand the structure of could with the following example.
Use of Could
The auxiliary verb could is used to show the possibility or ability of the past.
‘Could’ is used to talk about some possibility of the past about the freedom and ability to do something. For example:
I could sing properly when I was 12 years old.
Rohan could speak different languages.
When we arrived at the restaurant, we could not open the door.
Could you see what he was doing?
This auxiliary verb ‘could’ is also used for requests. Often ‘could’ is used in a form of questions to ask to do something. For example:
Could you tell me the direction where the hotel is, please?
Could you give me a book, please?
Be Able To
‘Be able to’ is not a modal verb. It is simply an adjective addition to a verb. Here the verb is an adjective followed by the infinitive. Sometimes ‘be able to’ is used instead of ‘can’ and ‘could’. ‘Be able to’ is used to show ability about something in a sentence. ‘Be able to’ can be used in all tenses. For example:
I was able to run.
I will be able to run.
I have been able to run.
‘be able to’ has an infinitive form. For example:
I would like to be able to play football better.
Structure of ‘Be Able To’
The basic structure for ‘be able to’ is as follows.
subject + be + able + infinitive (to)
Use of ‘Be Able To’
Following are the uses of ‘be able to’ with examples.
‘Be able to’ is used for showing ability in a sentence. We use it to express ability. The word ‘Able’ has an adjective meaning i.e. to have the power, ability, skill or means to do something. Hence ‘be able to’ can be used instead of ‘can’ or ‘could’ for ability.
The use of ‘be able to’ is possible in all tenses but we know that ‘can’ is used only in the present and ‘could’ is in the past for ability. ‘Can’ and ‘could’ do not have an infinitive form. Hence ‘be able to’ is used when other tenses or infinitives are used. Look at these examples:
I have been able to dance since I was ten. (present perfect)
Dinesh will be able to walk properly very soon. (future simple)
Komal would like to be able to drive a car. (infinitive)
Conclusion
So we have learnt about the modal auxiliary verbs and the use of ‘can and could’ with examples but ‘be able to’ is not an auxiliary verb. But it is convenient to learn about it here because it is often used as ‘can’ and ‘could’. We often use these in our normal sentences so we must be aware of their correct use.
FAQs on Can, Could, and Be Able To Explained With Examples
1. What are the main functions of 'can', 'could', and 'be able to' in a sentence?
The modal verbs 'can' and 'could', along with the phrase 'be able to', are primarily used to express concepts like ability, possibility, and permission. Their main functions are:
Ability: To describe if someone has the skill or capacity to do something (e.g., 'She can speak three languages.').
Possibility: To suggest that something is possible or could happen (e.g., 'It could rain tomorrow.').
Permission & Requests: To ask for or grant permission, or to make a request (e.g., 'Can I borrow your pen?' or 'Could you please open the window?').
2. What is the key difference between using 'can' and 'could' for ability?
'Can' is used to express ability in the present, while 'could' is used to express a general ability in the past. For example:
Present Ability (can): 'I can solve this puzzle.' (I have the ability now.)
Past Ability (could): 'When I was younger, I could run for miles.' (I had this general ability in the past.)
'Could' is also used for making polite requests and suggesting weaker possibilities in the present.
3. When is it necessary to use 'be able to' instead of 'can' or 'could'?
You must use 'be able to' in situations where 'can' or 'could' are grammatically incorrect. Since 'can' and 'could' are modal verbs, they don't have infinitive or future forms. Use 'be able to':
For future tenses: 'She will be able to join the team next month.' (Incorrect: 'She will can join...')
With other modal verbs: 'You might be able to get a discount.' (Incorrect: 'You might can get...')
For perfect tenses: 'He hasn't been able to finish his work yet.' (Incorrect: 'He hasn't could finish...')
Additionally, 'be able to' is often considered more formal than 'can'.
4. How is 'could' used to talk about possibilities in the present or future?
While 'could' often refers to the past, it is also frequently used to talk about present or future possibilities that are less certain or hypothetical. It implies a weaker possibility than 'can'.
Example: 'We could go to the cinema tonight if you're free.' (This is a suggestion or a possibility, not a definite plan.)
Example: 'Be careful, that glass could break.' (This indicates a possibility in the near future.)
This usage makes 'could' perfect for making suggestions and polite, tentative statements.
5. Which modal is more polite for making a request: 'can' or 'could'?
'Could' is generally considered more polite and formal for making a request. 'Can' is more direct and informal, suitable for friends and family. Using 'could' makes the request sound more indirect and less demanding.
Informal Request: 'Can you pass the salt?'
Polite Request: 'Could you please pass the salt?'
6. Why is it incorrect to say 'I can be able to do it'?
The phrase 'I can be able to' is grammatically incorrect because it is redundant. Both 'can' and 'be able to' express ability. Using them together is like saying the same thing twice in a row. You should choose one or the other based on the context.
Correct: 'I can do it.' OR 'I am able to do it.'
Incorrect: 'I can be able to do it.'
7. How is 'was/were able to' different from 'could' when talking about a specific past event?
This is a subtle but important difference. 'Could' refers to a general ability in the past, whereas 'was/were able to' refers to the ability to do something on a specific occasion (i.e., you not only had the ability but you also did it).
General Ability (could): 'He could swim well as a child.' (He had the general skill.)
Specific Achievement (was able to): 'Despite the rough waves, he was able to swim to the shore.' (He succeeded on that one occasion.)
In negative sentences, 'couldn't' and 'wasn't/weren't able to' are often interchangeable.
