Modals of Ability & Permission – Can, Could Be Able
Modals of Ability & Permission
We use the word can to talk about abilities and possibilities. We also use it make requests, or to ask for and give permission. Can is an auxiliary verb.
The sentence structure for using can is:
subject + can + main verb
Do not use to with the main verb when using can. It is always the bare infinitive so this sentence is incorrect “I can to go with you”. The sentence “I can go with you” is correct. Also, can is never conjugated.
|subject||auxiliary verb||main verb|
- There is only one form of can.
- The main verb is always the bare infinitive, without to.
Uses of Can
Can Used For Possibilities or Abilities
We use ”can” to talk about things we are able to do, or things that are possible:
- He can dance.
- I can drive you there.
- I cannot see the text. (I can’t see the text.)
- Can you help me?
We use can when discussing future ability. For example:
- Can you drive me to work tomorrow? (future)
- I can visit you next week. (future)
Can Used For Requests
We also use can informally to ask someone to do something. We are not asking if they have the capability to do something. For example:
- Can you pass me the sugar?
- Can you turn that down please?
- Can you please stop fidgeting?
- Can you stop yelling?
Can Used For Granting or Asking Permission
Sometimes we use can in place of “may” to ask or give permission informally:
- Can I drive your car?
- You can go out and play now.
Could is also an auxiliary verb. We use could to make requests and talk about past abilities or possibilities.
Structure of Could
The sentence structure for using the modal verb could is:
subject + could + main verb
When we use could the main verb is always the bare infinitive form, just like with can.
|subject||auxiliary verb||main verb|
|–||My grandfather||could not||read.|
|?||Could(auxiliary verb)||your parents(subject)||read?|
- The main verb is always the bare infinitive form, without to.
- There is only one form of could.
The sentence “my father could to fish” is incorrect while “my father could fish” is correct.
Use of Could
Could Used For Past Possibility or Ability
We also use could when referring to past possibilities. Here are a few examples of could for past possibilities:
- I could read when I was three.
- My father could juggle.
- We could not find the dog. (We couldn’t find the dog.)
- Could you understand what he was saying?
Could and couldn’t are used to refer to general abilities as well. If we are referring to a specific occasion, we use be able to and couldn’t. For example:
|Past General||Specific Occasion|
|+||My daughter could swim.||We were able to open the windows yesterday.|
|–||My father couldn’t swim.||We couldn’t open the windows the day before because it was too cold.|
Could Used For Requests
There are many times we use could when asking someone for something politely or formally:
- Could you help me find this shirt in a larger size?
- Could you please pass the salt and pepper?
Remember that even though we mentioned be able to, it is NOT a modal verb. We only mention it because it is sometimes used instead of can or could when talking about ability.
Structure of Be Able To
The structure of be able to is: subject + be + able + infinitive
|subject||be main verb||able adjective||infinitive|
|–||He||is not||able||to remember.|
|?||Are(be main verb)||you(subject)||able||to play.|
Be able to can be used in past, present and future tenses. For example:
- I was able to see my father yesterday.
- I will be able to come over tomorrow.
Be able to also has an infinitive form. Here are a few examples of be able to in the infinitive form:
- Someday, I would like to be able to go to Spain.
- He has to work hard to be able to get a raise.
Be Able To Used For Ability
We can also use the term be able to when discussing abilities. It can be used in place of the word can or could especially when we want to illustrate other tenses or the infinitive form.
- I have been able to drive for several years now. (present perfect)
- You will be able to drive when you are old enough. (future simple)
- I would like to be able to see the Great Pyramids someday. (infinitive)