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 -could is used to:

 

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

2) To express possibilities in the present. 

3) To make suggestions and conditional statements.  

4) To give and request permission (polite).

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

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The modal verb -could is used in the present and past tenses, it is used most often in affirmative statements to express possibilities in the present tense. 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 -could.

​Subject + could + main verb in the infinitive form

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

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

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​​​​​​​​​​      Examples

​​      Ex: We could do something else if you want. 

      Ex: She could make it to the train station on time yesterday. 

      Ex: I could get a better score next time. 

      Ex: When I was younger, I could watch cartoons all day. 

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Formation - Negative Statements 

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The modal verb -could is used in the present and past tenses, it is used most often in negative statements to express a subjects inability to complete an action in the past. 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 -could are typically formed using contractions. 

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

​Subject + could not + main verb in the infinitive form

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

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

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      Examples​

      Ex: I could not play baseball on Saturday, it was raining. 

      Ex: Couldn't we try something else? 

​      Ex: He couldn't win, his opponent is too good. 

      Ex: Right after the blizzard, we couldn't open our car doors. 

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Could uses 

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To express the ability a subject has to complete an action in the past

Note: The phrase be able to is used frequently in this context as well. 

     

      Examples

      Ex: My mother could not walk for 3 days after her surgery. 

      Ex: James could see well again after he got glasses. 

​      Ex: Could you get your car inspected on Saturday? 

      Ex: When my dog was a puppy he couldn't control his behavior. 

      Ex: Couldn't you visit the statue of liberty when you went to NY? 

      Ex: My phone could turn on after I replaced the battery 

      Ex: No one could figure out the answer of the last question on the test, it was too hard. 

      Ex: The event could continue when it stopped raining.

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      Examples - using be able to 

      Ex: My mother was not able to walk for 3 days after her surgery. 

      Ex: James was able to see well again after he got glasses. 

​      Ex: Were you able to get your car inspected on Saturday? 

      Ex: When my dog was a puppy he wasn't able to control his behavior. 

      Ex: Weren't you able to visit the statue of liberty when you went to NY? 

      Ex: My phone was able to turn on after I replaced the battery 

      Ex: No one was able to figure out the answer of the last question on the test, it was too hard. 

      Ex: The event was able to continue when it stopped raining.

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To express possibilities in the present

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

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      Examples

​      Ex: Breathing in too much smoke could harm your lungs.

      Ex: Doctor Daniels could perform complex cardio surgeries. 

​      Ex: Eating junk food once in a while couldn't make much of a difference. 

      Ex: Could working out a lot cause you to feel pain in your joints? 

​      Ex: She could be very kind or very unpleasant. 

​      Ex: Couldn't working too much lead to insomnia? 

​      Ex: Smoking at a gas station could cause an explosion. 

      Ex: Our lives could end at any moment. 

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To make suggestions and conditional statements 

Note: Negative statements are usually not used in this context​

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      Examples

​      Ex: We could go somewhere else. 

      Ex: I could help you carry your things to your door.  

​      Ex: You could try taking cough medicine. 

      Ex: Couldn't changing the system board help you fix your problem?

​      Ex: He could help you if you ask him. 

​      Ex: You could do anything if you work hard enough. 

​      Ex: Trying again couldn't hurt. 

      Ex: If lies kept you trapped, couldn't the truth set you free?

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To give and request permission (polite)

Note: Traditionally the modal verb -may is used in this context, however this has fallen out of use in modern English, the modal verb -can is also used in this capacity and sounds more informal than -could, however negative commands cannot be made with -could, we must use -can instead. Conditional statements may be used in this context. 
 

      Examples

​      Ex: You could begin now.

      Ex: Could I play video games if I finish my homework? 

​      Ex: Couldn't I go outside?

      Ex: You could hang out with your friends tonight, but come home at 11. 

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​​​​​​​​​​​​​​​​​​​​​​​Could-  Using -could at the end of statement to confirm information

               

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

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      Examples

      Ex: You could speak to her, couldn't you?

      Ex: James couldn't betray us, could he? 

      Ex: Cold dry wind could cause your lips to chap, could it not? 

      Ex: Lawyers could not lie to their clients, could they? 

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