Modal verbs are auxiliary verbs used to express ideas such as (necessity, ability, possibility, advice, obligation, probability, requests, permission, etc.), in English they are combined with verbs in their infinitive forms. Modal verbs have their own question and negation forms, they do not depend on the auxiliary verb -do for this purpose. Modal verbs in English include (-can, -could, -will, -would, -should, -must, -may, and -might), the modal verbs -ought to and -shall are antiquated and are not regularly used in modern English. 

 

The modal verb -can is used to:

 

1) To express the ability a subject has to complete an action. 

2) To express possibilities. 

3) To give and request permission (informal). 

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​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Formation - Affirmative Statements 

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The modal verb -can is only used in the present tense, it is used most often in affirmative statements to express a subject's ability to complete an action. Modal verbs are never conjugated depending on the subject, they remain the same for all subjects which makes them simple to use, modal verbs are always combined with a main verb in the infinitive form.  

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Structure used to form affirmative statements in the simple present ​with the modal verb -can.

​Subject + can  + main verb in the infinitive form

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Structure used to form affirmative questions in the simple present with the modal verb -can.​

​Can + Subject + main verb in the infinitive form?

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​​​​​​​​​​      Examples

​​      Ex: Charles can run 3 miles in 20 minutes.

      Ex: Can you speak Spanish?

      Ex: It can take up to 3 days for a check to clear. 

      Ex: Nurses can administer medication. 

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Formation - Negative Statements 

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The modal verb -can is only used in the present tense, it is used most often in negative statements to express a subjects inability to complete an action. Modal verbs are never conjugated depending on the subject, they remain the same for all subjects which makes them simple to use, modal verbs are always combined with a main verb in the infinitive form. Negative statements and questions in the present tense with the verb -be and modal verbs are not formed with the verb -do, they have their own question and statement forms. Negative questions are meant to express surprise, confirm information, or encourage agreement. Negative questions statements with the modal verb -can are typically formed using contractions. 

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Structure used to form negative statements in the simple present ​with the modal verb -can.

​Subject + cannot  + main verb in the infinitive form

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Structure used to form negative questions in the simple present with the modal verb -can.​

​Can + Subject + not + main verb in the infinitive form?

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      Examples​

      Ex: Mark cannot come to my birthday party. 

      Ex: They can't understand Russian. 

​      Ex: Can't you do that later? 

      Ex: It can't make that much of difference. 

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Can uses 

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To express the ability a subject has to complete an action

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      Examples

      Ex: My father can fly commercial aircraft.

      Ex: Frank cannot play the piano. 

​      Ex: They can't leave before the event ends. 

      Ex: Can Michael ride motorcycles? 

      Ex: Can't she write the email tomorrow? 

      Ex: Sea lions can dive more than 200 meters. 

      Ex: Can Jackie not get a new job? 

      Ex: Money can't buy happiness. 

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To express possibilities

​Note: Negative statements are usually not used in this context, however negative questions are.

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      Examples

​      Ex: Overly used engine oil can cause engine failure. 

      Ex: Ice on the roads can make cars lose control. 

​      Ex: He can do great things. 

      Ex: Can't changing the spark plugs fix the problem?

​      Ex: Mark can fold when under pressure. 

​      Ex: Can failure teach people how to do things better? 

​      Ex: Lit cigarettes can start fires. 

      Ex: Social media can hurt the mental health of children. 

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To give and request permission (informal)

Note: Traditionally the modal verb -may is used in this context, however this has fallen out of use in modern English, the modal verb -could is also used in this capacity and sounds more polite and formal than -can.     
 

      Examples

​      Ex: Can I use the bathroom?

      Ex: You can leave now. 

​      Ex: Can't I watch T.V.?

      Ex: You cannot start until I say so. 

​      Ex: You can't look yet. 

​      Ex: Can I put my things over there?

​      Ex: You can begin when you are ready. 

      Ex: Can I open a window? It's hot in here. 

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​​​​​​​​​​​​​​​​​​​​​​​Can -  Using -can at the end of statement to confirm information

               

The modal verb -can may be added to the end of a statement made with the modal verb -can to confirm information, note that affirmative statements use negative questions with the modal verb -can and negative statements use affirmative questions with the modal verb -can. 

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      Examples

      Ex: You can fix it, can't you? 

      Ex: He cannot sail a boat, can he? 

      Ex: Salt can't melt ice, can it? 

      Ex: Smoking can cause lung cancer, can it not? 

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Can -  Alternative phrase 

      

The phrase be able to can be used instead of the modal verb can. Unlike the modal verb can this phrase can be used in the past tense and the future tense making it very versatile. The biggest disadvantage of using the phrase be able to instead of the modal verb can in the present tense is that it must be conjugated to match the subject making it significantly more difficult than using -can. Like the modal verb can, the phrase be able to is combined with a main verb in the infinitive form.  

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Past 

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Examples of the phrase be able to in the past tense 

Note: The modal verb -could  can also be used in this context, however -could may cause more confusion than the phrase be able to in the past tense in affirmative sentences if a past time expression is not explicitly mentioned. 

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Ex: John was able to spend time with his family this past summer. 

Ex: We were able to finish the project after 2 months. 

Ex: The car wasn't able to start this morning. 

Ex: They weren't able to attend the wedding. 

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Comparison with the modal verb -could

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Ex: John could spend time with his family this past summer. 

Ex: We could finish the project after 2 months. 

Ex: The car couldn't start this morning. 

Ex: They couldn't attend the wedding. 

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Present 

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 Note: The modal verb -can sounds more natural than the phrase be able to in the present tense. 

 Ex: I am able to type about 50 words per minute. 

 Ex: The computer isn't able to turn on. 

 Ex: They aren't able to see anyone right now, they're in a meeting. 

 Ex: My car is able to go off-road. 

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Comparison with the modal verb -can

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 Ex: I can type about 50 words per minute. 

 Ex: The computer can't turn on. 

 Ex: They can't see anyone right now, they're in a meeting. 

 Ex: My car can go off-road. 

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Future 

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Examples of the phrase be able to in the future tense 

Note: This is only way to express the modal verb -can in the future 

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Ex: I will be able to relax this weekend 

Ex: They won't be able to watch the movie with us tonight. 

Ex: The team will be able to start over with a new coach. 

Ex: Most people think the governor won't be able to run for office again. 

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