Difference Between Must and Ought To

‘Must’ and ‘Ought To’ are those words that are used to emphasize a sentence or make it sound important legally and formally, respectively. The words have a very thin difference in them.


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Whenever a person wants to talk about the likelihood of an event, ‘Must’ and ‘Ought To’ both can be used, but it depends on how much the speaker is confident about happening of the event.

Must vs Ought To

The difference between ‘Must’ and ‘Ought To’ is ‘Must’ represents when an obligation is external or duty, whereas ‘Ought To’ refers to moral obligation. The emphasis is higher in ‘Must’ as compared to ‘Ought To’. ‘Must’ is a modal verb. A modal verb is used to express modality. ‘Must’ can refer to past tense when it is used with the present perfect of the principal verb. ‘Must’ makes the sentence forceful. ‘Ought To’ is a semi-modal verb. The usage of ‘Ought To’ makes the sentence sound less powerful. ‘Must’ is the most emphatic as compared to ‘Ought To’. The word ‘Ought To’ is not forceful like ‘Must’.

Must vs Ought To

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‘Must’ is used to express the need of the hour. It makes the sentence formal and legal. The degree of emphasis is highest when ‘Must’ is used in the sentence. ‘Must’ is used when the event is likely to happen. ‘Must’ is a modal verb.

‘Must’ is used when the probability of happening if the event is higher. ‘Must’ is always about strength in the sentence.

‘Ought To’ is a type of modal verb. It refers to something which is morally correct in a particular situation. It is mostly used when seeking suggestions or recommending something to someone. It refers to objective truth. ‘Ought To’ does not have any past form.

It is rarely used in questions and negatives. ‘Ought To’ is the semi-modals verb. ‘Ought To’ is used when the event may or may not happen.

Comparison Table

Parameters Of ComparisonMustOught To
MeaningUsed to express necessityUsed to express moral obligation
Degree Of EmphasisHighestComparatively high
Likelihood of the eventHighMay or may not happen
TonePowerfulLess powerful
Kind of verbModal verbSemi-Modal verb

What is Must?

‘Must’ is used to express obligation, duty, or compulsion. ‘Must’ do not changes its form with the tense, number, or the person of the subject. 

‘Must’ is a helping verb. It emphasizes the importance or need of something in a particular situation. ‘Must’ always signifies strong determination. The usage of ‘Must’ indicates that the speaker is certain that the subject will have executed the predicate.

It used to show a necessity.

The example is:

We must wake up early in the morning.

It is used to show logical probability, or probability is pretty high.

The example is:

That must be the postman.

It is used to hint at prohibition.

The example is:

One must not talk in the library.

It is used in an exclamatory sentence.

The example is:

You must be kidding!

It is used to strongly recommend something or advise something.

Whenever there is a need for emphasis and the level of emphasis is high, ‘Must’ is always used in the sentence.

It is used in directive requirements.

The example is:

The door handle must be rotated fully.

It is used to make an imperative sentence.

The example is:

You must arrive in class on time.

must 1

What is Ought To?

‘Ought To’ is different from other auxiliary verbs, which are followed by a to-infinitive. ‘Ought to’ generally point present and future time. It can refer to a past time when it is followed by the perfect infinitive (have + past participle). 

It is used to indicate when it is essential and right to do, referred to by the verb succeeding it.

The example is:

The students ought to be punctual at school.

It is used to indicate the probability of something that may happen.

The example is:

The seminar ought to increase awareness.

It is used to discuss those things which are long for or ideal.

The example is:

The government ought to make better traffic rules.

It is used to express duty.

The example is:

She ought to follow traffic rules.

Main Differences Between Must and Ought To

  1. ‘Must’ refer to the legal terminology of the sentence, whereas ‘Ought To’ is used by the speaker to sound formal.
  2. The degree of emphasis is higher in ‘Must’ instead of ‘Ought To’.
  3. ‘Ought To’ is used when we talk about moral duties, but ‘Must’ is used to express necessity.
  4. ‘Must’ is used in the sentence when the probability of happening is higher, whereas ‘Ought To’ is used when the probability of happening is not sure.
  5. ‘Must’ and ‘Ought To’ both are referred to as obligation but ‘Must’ is for external obligation, and ‘Ought To’ refers to moral obligation.
Difference Between Must and Ought To
  1. https://link.springer.com/content/pdf/10.1007/BF00353453.pdf
  2. https://books.google.com/books?hl=en&lr=&id=denentJbyQoC&oi=fnd&pg=PA127&dq=ought+to+&ots=t1dUlQkPK-&sig=RxMx63yEpXwc99OVvY2LKgZq3aw
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