Use of Must and Should

Use of Must

Definition: The modal verb must is most often used to express necessity—i.e., that something has to happen or be the case. We also use this sense of the word to indicate a strong intention to do something in the future, to emphasize something positive that we believe someone should do, and to rhetorically introduce or emphasize an opinion or sentiment. In addition to indicating necessity, must can be used to indicate that something is certain or very likely to happen or be true.


When must indicates that an action, circumstance, or situation is necessary, we usually use it in a declarative sentence. For example:

  • This door must be left shut at all times!
  • We absolutely must get approval for that funding.
  • You must not tell anyone about what we saw.
  • Now, you mustn’t be alarmed, but we’ve had a bit of an accident in here.

We can also use must in interrogative sentences to inquire whether something is necessary, usually as a criticism of some objectionable or undesirable action or behavior. For instance:

  • Must we go to dinner with them? They are dreadfully boring.
  • Must you be so rude to my parents?
  • Must I spend my entire weekend studying?

However, this usage is generally reserved for more formal speech and writing, and isn’t very common in everyday English.

Indicating Strong Intention

We use the same meaning of must to indicate something we have a very strong intention of doing in the future. For example:

  • I must file my taxes this weekend.
  • I must get around to calling my brother.
  • We must have the car checked out soon.

Emphasizing a Suggestion

We also use this meaning to make suggestions to others of something positive we believe they should do, as in:

  • You simply must try the new Ethiopian restaurant on 4th Avenue—it’s fantastic!
  • It was so lovely to see you. We must get together again soon!
  • You must come stay with us at the lake sometime.

As a Rhetorical Device

Finally, we can also use this meaning of must as a rhetorical device to politely introduce or emphasize an opinion or sentiment about something:

  • I must say, this has been a most wonderful evening.
  • And I must add that Mr. Jones has been an absolute delight to work with.
  • I must be clear: we will disavow any knowledge of this incident.

Note that we can accomplish the same thing by using the verbs let or allow instead, as in:

  • Let me be clear: this decision is in no way a reflection on the quality of your work.
  • Allow us to say, we were greatly impressed by your performance.

Certainty and Likelihood

In addition to being used to indicate a necessary action or situation, must is also often used to describe that which is certain or extremely likely or probable to happen, occur, or be the case. For example:

  • You must be absolutely exhausted after your flight.
  • Surely they must know that we can’t pay the money back yet.
  • There must be some way we can convince the board of directors.
  • I must have left my keys on my desk at work.
  • Speaker A: “I just got back from a 12-week trip around Europe.”
  • Speaker B: “Wow, that must have been an amazing experience!”

Generally speaking, we do not use the negative of must (must not or mustn’t) to express a negative certainty or strong disbelief. Instead, we use cannot (often contracted as can’t), as in:

  • You can’t be tired—you’ve been sleeping all day!
  • I can’t have left my phone at home, because I remember packing it in my bag.
  • After three years of college, she wants to drop out? She cannot be serious.

Definition: The modal auxiliary verb should is used to politely express obligations or duties; to ask for or issue advice, suggestions, and recommendations; to describe an expectation; to create conditional sentences; and to express surprise.

There are also a number of uses that occur in British English that are not common in American English.

Use of Should

Polite Obligations

Should is used in the same construction as other modal verbs (such as will, shall, and must) to express an obligation or duty. However, whereas must or will (and even shall) make the sentence into a strict command, which might appear to be too forceful and could be seen as offensive, should is used to create a more polite form that is more like a guideline than a rule. For example:

  • “Guests should vacate their hotel rooms by 10 AM on the morning of their departure.”
  • “I think she should pay for half the meal.”
  • “You shouldn’t play loud music in your room at night.”
  • “I think healthcare should be free for everyone.”
  • “She should not be here; it’s for employees only.”

Asking the Reason Why

We can follow the question word why with should to ask the reason for a certain obligation or duty. For instance:

  • “Why should I have to pay for my brother?”
  • “Why shouldn’t we be allowed to talk during class?”

Advice and Recommendations

Should can also be used to issue advice or recommendations in much the same way. For instance:

  • “You should get a good map of London before you go there.” (recommendation)
  • “You shouldn’t eat so much junk food—it’s not good for you.” (advice)

We can also use should in interrogative sentences to ask for someone’s advice, opinion, or suggestion, as in:

  • “What should I see while I’m in New York?”
  • “Should she tell her boss about the missing equipment?”
  • “Is there anything we should be concerned about?”


Using should in affirmative (non-negative) sentences can be used to express an expected outcome, especially when it is followed by the verb be. For example:

  • “She should be here by now.”
  • “They should be arriving at any minute.”
  • “I think this book should be interesting.”

We can also follow should with other verbs to express expectation, but this is less common. For instance:

  • “They should find this report useful.”
  • “We should see the results shortly.”

If we use the negative of should (should not or shouldn’t), it implies a mistake or error, especially when we use it with a future time expression. For example: •

  • “She shouldn’t be here yet.”
  • “He shouldn’t be arriving for another hour.”

We normally do not use should not to refer to expected future actions like we do in the affirmative; it generally refers to something that just happened (in the present or immediate past).

Should vs. be supposed to vs. be meant to

In many instances, should can be replaced by be supposed to or be meant to with little to no change in meaning. For instance, we can use be supposed to or be meant to in place of should for something that is expected or required to happen. For example:

  • “He should be here at 10 AM.”
  • “He is meant to be here at 10 AM.”
  • “He is supposed to be here at 10 AM.”

We can also use these three variations interchangeably when asking the reason why something is the case. For instance:

  • “Why should I have to pay for my brother?”
  • “Why am I meant to pay for my brother?”
  • “Why am I supposed to pay for my brother?”

However, when we are expressing an obligation or duty, we can only replace should with be supposed to or be meant to when it is in the negative. For instance:

  • “You shouldn’t play loud music in your room at night.”
  • “You aren’t meant to play loud music in your room at night.”
  • “You aren’t supposed to play loud music in your room at night.”

In affirmative sentences in which should expresses an obligation or duty (as opposed to an expectation), these verbs are not interchangeable. For instance:

  • “I think she should pay for half the meal.” (obligation)
  • “I think she is supposed to pay for half the meal.” (expectation)
  • “I think she is meant to pay for half the meal.” (expectation)

Be supposed to and be meant to are also used to express general beliefs, which is not a way we can use the modal verb should. For example:

  • “He is supposed to be one of the best lawyers in town.” (general belief)
  • “He is meant to be one of the best lawyers in town.” (general belief)
  • “He should be one of the best lawyers in town.” (obligation)

We can see how the meaning changes significantly when should is used


Conditional Sentences

Should can be used in conditional sentences to express an outcome to a possible or hypothetical conditional situation. Sometimes we use should alongside if to create the conditional clause, as in:

  • If anyone should ask, I will be at the bar.”
  • If your father should call, tell him I will speak to him later.”

We can also use should on its own to set up this condition, in which case we invert it with the subject. For example:

  • “Should you need help on your thesis, please ask your supervisor.”
  • “The bank is more than happy to discuss financing options should you wish to take out a loan.”

Expressing Surprise

Occasionally, should is used to emphasize surprise at an unexpected situation, outcome, or turn of events. We do so by phrasing the surprising information as a question, using a question word like who or what and often inverting should with the subject. (However, the sentence is spoken as a statement, so we punctuate it with a period or exclamation point, rather than a question mark.)

The “question” part of the sentence is introduced by the word when, with the “answer” introduced by the word but. For example:

  • “I was minding my own business, when who should I encounter but my brother Tom.”
  • “The festival was going well when what should happen but the power goes out!”

Uses of should in British English

There are a number of functions that should can perform that are more commonly used in British English than in American English.

Several of these are substitutions of would, while other uses are unique unto themselves

Should vs. would in British English: There are several modal constructions that can either take would or should. American English tends to favor the modal verb would in most cases, but, in British English, it is also common to use should, especially to add formality.

Polite Advice

We can use should/would in the first person to politely offer advice about something. (It is common to add the phrase “if I were you” at the end, thus creating a conditional sentence.) For example:

  • “I should/would apologize to the boss if I were you.”
  • “I shouldn’t/wouldn’t worry about that right now.”

Expressing Desires

We can use either should or would with the main verb like in the first person to express or inquire about a person’s desire to do something. (We can also use the main verb care for more formal or polite sentences.) For example:

  • “I should/would like to go to the movies later.”
  • “We shouldn’t/wouldn’t care to live in a hot climate.”
  • “I should/would like a cup of tea, if you don’t mind.”
  • “I don’t know that I should/would care for such an expensive house.”

Asking the Reason Why

In addition to asking the reason why a certain obligation or requirement is the case, we can also use should in the same way as would to ask the reason something happened or is true. For instance:

  • “Why should/would my brother lie to me?”
  • “Why should/would they expect you to know that?”

If we use I or we as the subject of the question, it is often used rhetorically to suggest that a question or accusation is groundless or false, as in:

  • “Why should/would I try to hide anything from you?”
  • “Why should/would we give up now, when we’ve come so close to succeeding?”

To Show Purpose

 Should and would can also be used after the phrase “so that” and “in order that” to add a sense of purpose to the main verb, as in:

  • “I brought a book so that I shouldn’t/wouldn’t be bored on the train ride home.”
  • “He bought new boots in order that his feet should/would remain dry on the way to work.”

After Other Words and Phrases

There are several instances in British English in which should is used after the relative pronoun that or certain other phrases to create specific meanings, especially in more formal language.

To express an opinion or feeling

When we use a noun clause beginning with that as an adjective complement, we can use should in it to express an opinion or sentiment about what is said. For example:

  • “It’s very sad that she should be forced to leave her house.”
  • “Isn’t it strange that we should meet each other again after all these years?”

Conditional Circumstances

Similarly, should can be used after the phrases for fear (that), in case (that), and (less commonly) lest (that) to demonstrate the possible conditional circumstances that are the reason behind a certain action. For example:

  • “I always pack my rain jacket when I cycle for fear (that) it should start raining midway.”
  • “You should pack a toothbrush in case (that) you should be delayed at the airport overnight.”
  • “She makes sure to set the alarm before leaving lest (that) someone should try to break in.

Thanks for reading about “use of must and should”.

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