Difference Between Should Be and Must Be

The words ‘should be’ and ‘must be’ are stated under modal auxiliaries according to the English language that is supposed to be used correctly since there does exist a difference between should be and must be.

Both these words differ in their meaning and characteristics within their form too.

Should Be vs Must Be

The main difference between should be and must be is that ‘should be’ is often used to express feelings related to a probability of happening or a recommendation. On the other hand, ‘must be’ is actually used to represent the feeling of a particular obligation or duty towards a specific thing.

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‘Should be’ is said to be a modal auxiliary and is used to express the possibility that something could happen in the future. ‘Should be’ is stated as a goal that is undesirable in nature.

Should be is used only as a verb, and it got its origin from the word, ‘sceolde’, which is an old English word.

‘Must be’ is said to be a modal auxiliary used to express and state a duty to be done or an unavoidable obligation. The word must be is used in nearly about three contexts with three totally different meanings.

‘Must’ was originated from an old English word called ‘Moste’.

Comparison Table Between Should Be and Must Be

Parameters of comparison Should BeMust Be
MeaningThis is used to state an obligation or a duty of a person in a sentence. This also states that what is the best thing to do in a specific case in a sentence.This word is used to state a certainty or a compulsion of something to be done in present or future in a sentence.
Degree of comparisonWhen this word is used in a sentence, the degree of comparison is quite low.When this word is used in a sentence, the degree of comparison is the highest.
FunctionStated for giving advice or feedback.Stated for telling something is compulsory to happen.
DerivationIt was derived from the word “sceolde”.It was derived from the word “moste”.
NatureUsually used in informal communication.Usually used in formal or legal communication.

What is Should Be?

A person usually uses the word should be to state particular duties and obligations for a person. A person also uses ‘should be’ when a thing has to be done in that specific situation only, especially when it comes to judging someone’s activities.

‘Should be’ is used as the past tense of shall be, which is in the future tense. ‘Should be’ often is used to state a piece of advice or a recommendation or talk about something that is generally said to be right or wrong within certain limits.

There are specific fundamental ways where the word should be is to be used in a sentence.

  1. To tell which is the best choice when something is happening.
  2. If there is a certain chance of something happening.
  3. To give specific or seek a bit of specific advice.
  4. To give and ask a particular reason for something happening.


  1. She should be going to school today since it’s not a holiday.
  2. She should be sleeping early today because she has to wake up early tomorrow.
  3. They should probably drop her home since it’s actually too late
  4. I hope I should be reaching on time for office since the trains are late today.

What is Must Be?

The word ‘must be’ was initially used to express an obligation to do something. This word is used to denote that something is compulsory and it has to happen for sure strongly.

The word must be is used as a helping verb in a sentence. This word strongly emphasizes the need for a specific thing to happen in a sentence by stating it.

When a person says it, he means that it is a compulsion for something to happen and cannot be unfulfilled.

There are specific important ways where the word must be is to be used in a sentence.

  1. When a person wants to express a firm action.
  2. When a person states or expresses prohibition of something.
  3. When a person wants to give particular feedback of reviews regarding something
  4. Used in exclamatory sentences.
  5. When a person wants to emphasize strongly that a particular thing has to happen.


  1. This must be so amazing!
  2. You must be kidding.
  3. I must be going, for it is already late.
  4. This dish must be served with ice cream.
  5. The driver must park the car after dropping them.

Main Differences Between Should Be and Must Be

  1. The word ‘should be’ denotes a possibility of something happening, whereas the word ‘must be’ is used to represent a certainty.
  2. The term ‘should be’ indicates that something can happen, whereas the word ‘must be’ suggests that something has to indeed occur.
  3. ‘Should be’ is certainly used to give a piece of advice. On the other hand, ‘must be’ denotes a compulsion of something.
  4. The word ‘should be’ is usually used in an informal conversation, whereas the word ‘must be’ is used in legal and formal ways.
  5. The degree of emphasizing is more minor in ‘should be,’ whereas the element of emphasis is the highest in ‘must be.’


The words ‘should be’ and ‘must be’ both are used to state a certainty of something, and the only difference is that in ‘should be,’ the degree of emphasis is more minor, whereas in ‘must be,’ the force is more and is stated strongly.

‘Should be’ is used to tell that something can happen, whereas ‘must be’ is used to denote a duty or an obligation. Both these words are modal verbs and helping verbs which are put into a sentence.

Both ‘should be’ and ‘must be’ are used in sentences having their characteristics and functions to be performed, giving two different meaning to a sentence.

They describe the necessity of something, and yet if they are replaced with each other, then the entire meaning of a sentence could actually change.


  1. https://www.jstor.org/stable/4176299
  2. https://journals.sagepub.com/doi/abs/10.3102/0013189X033001027
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