Function + Modal & Tense

• Can indicates if someone is able to do something or not in the present.
  
  

• Could is employed to talk about past ability.
  
  

• Negative forms:  cannot (can’t), could not (couldn’t)

Examples

• Can you program?

  • Yes, I can.  I can program in many languages.

  • No, I can’t.  I cannot program at all.

• Could you stay out late when you were young?

  • Yes, I could.  I could stay at a friend’s until 10.

  • No, I couldn’t.  I could not stay out past 7.

• I slept rather poorly—I could hear you two arguing all night.

Function + Modal & Tense

• May, can and could are used with “I” and “we” in a question to ask permission.
  
  

• Can, could and would are used with “you” in a question.

• Refusing permission: could is not used to refuse permission.

• Might can be used to request permission in formal settings; however, "may" or "may not" is used in reply to the question. "Might" can also be used as a suggestion.
  
  

• Negative forms:  may not (Ø), cannot (can’t), could not (couldn’t), would not (wouldn’t). This form can be used as a reproach to request that someone stop doing something undesirable, or to do something they are not doing that we want them to do.
  
  

• Casual versus formal:  can is considered casual speech and should not be used in formal situations.

• Notes:

  • can is considered casual speech and should not be used in formal situations;

  • the two words will you can be used for a limited number of phrases as a less polite or less formal method of using "would."

Examples

• Hey buddy, can I get you a slice of pizza?

• Sir, could I offer you some tea?

• Ma’am, may I offer you some tea?

• No thank you.  May I have some water instead? No you mayn't.

• Might I get you a crumpet? Yes, you might may.

• You might want to try that with some raspberry jam.

• Could I also get some biscuits with that, please?

• Mom, can we go out to a restaurant tonight?

• Can you turn down the music Fred?

• Can’t you turn down the music, Fred? Why can’t you be nice?

• Could you have that delivered to me? Yes, I can. No, I can’t. Yes, I could No, I couldn't.

• Could I not do everyone’s laundry for them?

• Would you mind passing the butter please?

• Would you please not shout so loud?
  
  

• You can't park there.
  
  

• Jack, will you get the door for me, please?

• Sir, will would you like me to unpack your bags for you?

Function + Modal & Tense

• Must is used when something is compulsory or absolutely required.

• Need can be used in a modal form when asking questions.

• Need also has a rare use where it is paired with a negative word or phrase (e.g. no one, nobody, nothing).

• Have to and had to express obligation when acting in a modal form.*

• Need to, is used when an action is required to reach a specific objective or fulfill a condition when acting in a modal form.*

• Had to shows obligation in the past. It is the past form of "must."
  
  

• Must not is used when there is an obligation NOT to do something (forbidden). That is to say, there is a requirement to abstain from something.
  
  

• Do not have to and does not have to (don’t have to, doesn’t have to) is used when there is no obligation to do something.  It means that it is your choice (voluntary).

• Need not (needn't) is the same as "do not have to." It gives permission to someone not to do something.

• Did not have to (didn’t have to) is used when referring to something in the past.
  
  

• Future form:  will have to and will need to are used more than "must" to express future obligations. "Must" is sometimes used to make general or personal references to the future.

Examples

• Mr. Spence, you must always arrive on-time for work.

• Johnnie, you have to look both ways before you cross the street.*

• Must she concentrate more  on her studies?

• She had to appear in court yesterday. She has to appear in court today.*

• Need he continue?  No one need know his identity.

• He needs to continue if he wants to pass the course.*

• The judge told Ellis that she had to complete her community service before last Saturday.
  
  

• You must not drive on the right-hand side of the road in England.

• Your doctor told you that you must not return to work.
  
  

• You do not have to submit your taxes until March.

• He does not have to join the army because he has a severe case of asthma.

• You needn't concern yourself with the details. Just sign.

• You needn't have given her the money.  It was unnecessary. She doesn't need it.

• I don’t have to eat spinach if I don’t want to.

• You did not have to buy her such an expensive present!
  
  

• She will have to file her taxes before April.*

• They will need to work harder if they want to enter college.*

• I must not forget to follow instructions next time.

* Note:  “have to” and "need to" are not modal auxiliaries; however, they are included here because they act like modals (they act similar to “must”). Unlike true modals, these verbs (along with "be able to" and "be going to") change form to agree with the subject, such as adding an “s” in the third-person singular form. People use “have to” when they want to talk about obligations—things they have no choice about doing. However, they use “need to” when they want to talk about things that are necessary to do in order to achieve a certain goal or for something else to happen.

Function + Modal & Tense

• Should and ought to are  used for:

  • giving advice (it is a good idea to …);

  • expressing a moral obligation; or

  • expressing an ideal situation.

• Would can be used to offer advice less directly with verbs such as advise, imagine, recommend, say, suggest, and think.
  
  

• Negative forms:  should not (shouldn’t), ought not to (oughtn’t to)
  
  

• Past forms: “should have + the past participle” or “ought to have + the past participle”
  
  

• Note: "ought to" is less common and more formal than "should."

Examples

• You should always begin preparations for an English essay several days before the due date.

• They ought to pay attention when operating such heavy equipment.

• We ought to have told him instead of keeping it a secret.

• We ought to have told him instead of keeping it a secret.

• I would recommend that we stay here until the rain passes.
  
  

• You should not drive your vehicle when there’s a blizzard. 

• They ought not to have climbed the fence.
  
  

• Should she be worried?

• Ought she to be concerned?

• We should have frozen the meat.

Function + Modal & Tense

• Would can be used to express:

  • an action that is conditional upon something;

  • a desire to have or to do something;

  • something that was done habitually in the past; and

  • the future from a past perspective.
    
    

• Negative form:  would not (wouldn’t)

• Notes:

  • use the words “would like to” express desire; and

  • people use used to to talk about states of being in the past instead of "would."

Examples

• If I had a pen, I would take notes.

• I would like to become a lawyer.

• When I was young, I would swim all summer long.

• When I was young, I thought that I would become a pilot.
  
  

• If I had money, I would not be here right now.

• I wouldn’t want to be in her shoes.

• When I was young, I wouldn’t get up until 8 am. 

• When I was young, I used to live in New Brunswick. 

Function + Modal & Tense

• Will (I'll, he'll, you'll, she'll, they'll, it'll) is used to express certainty, general truths, and habits.

  • Note: Will is also used to express the future.
    
    

• Must can also be used to express probability.  It is usually a deduction made by someone.

• Must have expresses a deduction about something in the past. The past form is “must have + the past participle”.
  
  

• Should and ought to express strong possibility.

• Can, could and may express possibility.

• Might also indicates possibility; however, it usually means less of a possibility than “could” or “may”. There is a weak possibility.
  
  

• Cannot (can’t) means that something is not at all possible. It can be used as a negative form of "must."
  
  

• Negative forms:  will not (won’t), must not (mustn’t), could not (couldn’t), might not (mightn't), may not (Ø)
  
  

• Regret / disapproval / criticism: use “could have + the past participle.” People also admonish other people with the "How could you?" expression.
  
  

• Notes:

  • "ought to" is less common and more formal than "should;"

  • A noun phrase + ’ll is normally unacceptable in formal writing; for example, it is considered informal to write that "Mother'll be late."

Examples

• He will drown if he tries to swim across the Atlantic. He'll die.

• The baby will get upset if you try to feed it lemon juice.

  • I will get up early tomorrow for work. (example of "will" used for future tense rather than habit or certainty)

• An hour has passed.  She must be at home by now.

• There must be a fire in here somewhere.  I can smell smoke.

• I saw that candy dish was empty yesterday. The children must have eaten all of the candy.
  
  

• We should arrive tomorrow, unless the flight gets cancelled.

• The opera ought to begin in five minutes.

• We can go on vacation if we decide to because I've accumulated enough vacation days.

• That electric motor may short-circuit if you don't dry it properly.

• You should sterilize that and put a bandage on it.  Otherwise, it could get infected in this dirty environment.

• He could have slept over instead of driving home. 

• My aunt might visit today.  I’m really not sure, though.
  
  

• You can’t possibly be serious! I won’t eat that.

• You mustn’t press the red button.

• This cup must be yours. It can't be mine—my name is not on it.

• I couldn't have reached that. I'm too short.
  
  

• You could have warned me. I could have been hurt.

• How could you have betrayed me this way?!