Shall Be vs Must Be: Difference and Comparison

A verb indicates the actions of a person. In English, verbs are of two types one is the main verb that describes the direct activities of a person, and the other is an Auxiliary verb that describes the mood, tense, and aspect voice of a person.

Auxiliary verbs are complicated to construct. There are three types: primary auxiliary verbs, modal verbs, and semi-modal verbs.

“Shall” and “Must” are modal auxiliary verbs. These verbs are combined with “be” in different tenses to express intentions, futurity, advice, and others.

Key Takeaways

  1. Shall be and must be both indicate mandatory requirements, with shall be being more formal than must be.
  2. Shall be is commonly used in legal documents and contracts, while must be is used more in various contexts.
  3. The use of shall be implied a stronger obligation than must be, but both express a requirement that must be fulfilled.

Shall Be vs Must Be

The term ‘shall be’ is used to specify future actions. This term is used in future tenses. For example, I shall be cooking meat tomorrow. This example shows an activity that a person will perform in the future. The term ‘must be’ can have multiple uses. It can be used to give orders to someone. It can also be used to give advice. 

Shall Be vs Must Be

Shall be is used to question someone. Shall be used only with I and We subjects.

Shall be is also replaced with “Will be” in some situations. “Shall be” is used mainly in Future continuous tense to express positive and negative sentences.

“Shall be” is hard to construct and is used in written English more than in conversation. “Shall be” has a present participle as the main verb.

The structure of “Shall Be” is

Subject + shall + be + ing form (main verb) -affirmative sentence

Subject + shall + not + be + ing form (main verb) – negative sentence

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“Must be” advises, concludes, orders, and suggests. Both “Shall be” and “Must be” are followed by present and past participles. “Must be” is formally used in English conversation. “Must be” is easy to construct and understand. The structure of “Must be” is

Subject + Must+ be+ present or past participle -affirmative sentence

Subject + Must+not+ be+ present or past participle -negative sentence

Comparison Table

Parameters of ComparisonMust beShall be
Tense‘Must be’ is used in the simple present and future tense.‘Shall be’ is used in the future continuous tense.
Meaning‘Must be’ expresses obligations, necessity, and probability, to give order and advice.‘Shall be’ expresses futurity, possibility, suggestions, and commitments.
Subject‘Must be’ is used with any subject.‘Shall be” is used with I and We only. 
Contracted FormThere is no contracted form for Must. Must not plus be is written as Mustn’t be.‘ll be for Shall be and Shan’t be for Shall not be.
ExampleHe must be playing Cricket.I shall be late tomorrow.  

What is Shall Be?

Future continuous tense is used to construct a sentence communicating future actions at a particular time. “Shall be” is a modal auxiliary verb that helps convey a subject’s emotions, like futurity, suggestions, commitment, and willingness.

It is used to question me and We subject. “shall be” is also being replaced with “will be” phrasal verb. “shall be” is used formally in communication.

It is used mainly in written documents like policies, procedures, government or business plans, and others to indicate dedication. Some of the examples of “Shall be” usage in the future tense are

Affirmative Sentence

I shall be attending a meeting in Mumbai next week.

We shall be playing carom at this time tomorrow.

 Negative Sentence

I shan’t be at home tomorrow.

I shan’t be coming to your wedding next week. I am leaving for Hyderabad tomorrow. 

Shall be is not used to interrogate someone, Will be is used instead. Shall be is preferred only in written language mostly.

shall be

What is Must Be?

“Must” is a modal auxiliary verb used in the present and future tense to convey command, advise, suggest, and describe beliefs, assumptions, and necessity. “Must” verb is used in any sense, but “Must be” is used in the present or future tense.

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Preset tense talks about current or general situations, and future tense discuss future actions. The phrasal verb “Must be” is followed by either present or past participle.

“Must be” has a similar meaning to Have to. Have to is a semi-auxiliary modal conveying obligations, necessity, and order. Some of the examples of the phrasal verb “Must be” are

Affirmative sentence

It must be freezing in Kashmir.

The Articles must be written as per guidelines.

Negative sentence

You must not be late for the party.

They must not be relatives.

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Main Differences Between Shall Be and Must Be

  1. The Phrase “Shall be” conveys emotions like willingness, commitment, intentions, and futurity. The phrasal verb “Must be” convey advice, order, obligations, necessity, and possible conclusions.
  2. “Shall be” is used in future continuous tense, and “Must be” is used in present and future tenses.
  3. “Shall be” is used with I and We subjects, whereas “Must be” is used with any subject.
  4. “Shall be” is rarely used in conversation. “Must be” is easy to use in conversations to express obligations.
  5. “Shall be” and “Will be” have the same features and usage. “Must be” and “Have to” have the same features and usage.
Difference Between Shall Be and Must Be

Last Updated : 11 June, 2023

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22 thoughts on “Shall Be vs Must Be: Difference and Comparison”

  1. I never really thought about the differences between ‘shall be’ and ‘must be’ until reading this article. It’s very thorough and eye-opening.

  2. This is a really informative article. I think it does a really great job of explaining the nuances of modal verbs in English. Cardinal and dynamic modals NEED to be understood in order to properly understand the English language.

  3. The comparison table is really useful in helping to understand the differences between ‘must be’ and ‘shall be’.


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