flowexam.com teacher explaining in English obligation modals with examples for TOEIC® preparation

Guide to Obligation Modals – TOEIC® Preparation

Flow Exam team

Whether expressing a personal constraint, a necessity imposed by standards, or particular situations, modals are fundamental linguistic tools in everyday, professional, and academic communication. This guide details the main modals must, have to, and shall, as well as alternative structures such as need to and be supposed to, to allow you to select the most appropriate phrasing depending on the context of use.

1. lockquote{Must}: Expressing Strong Obligation

A. In Which Situations to Use lockquote{must}?

Must is the reference modal for formulating an obligation. It is mainly used to convey:

  • Intense personal constraint: the speaker considers an action absolutely essential.
    • You must quit smoking for your health.(The speaker strongly insists on the necessity of quitting smoking.)
  • An obligation originating from the speaker themselves, rather than external rules or third parties.
    • I must complete this report before tomorrow.(The subject considers it crucial (according to their own judgment) to finalize this report before tomorrow.)

B. lockquote{Must not}: Formulating a Prohibition

The negation of "must" is "must not" (contraction: "mustn't"), which conveys formal prohibition or the obligation to refrain from performing an action.

  • You mustn't open this door under any circumstances.(You are forbidden to open this door; it is prohibited.)
  • He mustn't disclose that information.(He is strictly forbidden from revealing this information.)
To delve deeper into this point, consult our guide on modals - expressing prohibition

C. lockquote{Must} in the Interrogative Form: Formal Usage

Although infrequent, the use of "must" in the interrogative form exists, mainly in a formal or literary register:

  • Must I really attend the entire conference?(Is it truly essential that I attend the entire conference?)

2. lockquote{Have to}: Translating External Obligation

A. When to Use lockquote{have to} and lockquote{has to}?

"Have to" (and its variant "has to" in the third person singular) is used to express:

  • An obligation coming from the outside, such as a rule or a circumstance that compels action.
    • I have to renew my passport soon.(Constraint imposed by administration or legislation, not by the speaker.)
  • A factual or general necessity.
    • She has to call her boss before 6 p.m.(Obligation dictated by the professional context; it is not a personal choice.)

B. lockquote{Must} or lockquote{have to}: How to Choose?

Semantic Distinction

"Must" and "have to" are both translated as "devoir" in French, but their meaning differs. Here is the essential nuance:

  • "Must" conveys an obligation originating from the speaker (their judgment or own will)
  • "Have to" conveys an obligation imposed from the outside (legislation, rule, situation)

Temporal Distinction

Unlike "must", which is limited to the present tense, "have to" is conjugated across all verb tenses.

Past had to I had to wake up early yesterday.She had to finish her homework last night. Present have to / has to I have to leave now; I'm running late.She has to attend the meeting at 10 AM. Future will have to I will have to prepare for the exam tomorrow.She will have to submit the application next week. Present Perfect have had to / has had to I have had to change my plans because of the rain.She has had to work overtime to meet the deadline. Conditional would have to I would have to leave early if the train is late.She would have to cancel her trip if it rains. Past Conditional would have had to I would have had to take a taxi if the bus hadn't arrived.She would have had to study harder to pass the exam.

C. lockquote{don't have to}: Signalling the Absence of Obligation

"Don't have to" is used not to formulate a prohibition, but to signify the absence of obligation or necessity.

  • You do not have to come if you're busy.(You are not compelled to come; it is not a prohibition, simply no obligation.)
  • He doesn't have to work on weekends.(He is not required to work on weekends.)
To learn more, consult our guide on modals - expressing absence of obligation

3. lockquote{Shall}: Strict Obligation in Formal Contexts

In official documents, contracts, legislative texts, or regulations, shall is frequently used to formulate a strict obligation. In these contexts, its strength is equivalent to must.

  • The tenant shall pay the rent on the first day of each month.(Contractual or legal obligation.)
  • Employees shall comply with the company's code of conduct.(Formal obligation arising from a regulation.)

In a formal or archaic register, shall can also express an obligation, although today it is generally replaced by must or have to in contemporary English.

  • You shall not pass.(Absolute obligation or prohibition (old or solemn style))
  • Each participant shall bring their own equipment.(Obligation applying to all participants (formal register))

4. The Pure Modal lockquote{need}: Limited Usage

The use of the pure modal "need" remains rare, mainly reserved for a formal register and negative or interrogative forms. In practice, the semi-modal "need to" is generally preferred.

  • Need I really apologize?(Formal and dated; one would prefer lockquote{Do I really need to apologize?})
  • You needn't worry.(Formal; one would rather say lockquote{You don't need to worry.})

5. The Semi-Modal lockquote{need to}: Expressing Necessity

A. In Which Situations to Use lockquote{need to}?

"Need to" is used to indicate that there is a necessity or a need to accomplish something. "Need to" is close to "have to", but often carries a more personal dimension.

It expresses a required action due to a given situation or because it is logically necessary, rather than due to a rule or law.

  • I need to buy groceries; the fridge is empty.(Necessity arising from the situation: the empty fridge.)
  • She needs to prepare for her exam tomorrow.(Necessity imposed by the imminent exam.)

B. lockquote{don't need to}: Absence of Necessity

One can use "do not need to" (or "don't need to") to signify the absence of obligation or necessity.

  • You don't need to hurry; we have plenty of time.(You don't need to hurry; we have all the time we need.)
  • He doesn't need to attend the meeting if he's busy.(He is not required to attend the meeting if he is busy.)
To learn more, consult our guide on modals - expressing absence of obligation

6. lockquote{Should} / lockquote{ought to}: Advice and Light Obligations

A. In Which Situations to Use lockquote{should} and lockquote{ought to}?

"Should" and "ought to" are used to express:

  • Advice or recommendation.
  • Sometimes, attenuated obligation or strong suggestion.

Although these two semi-modals have very similar meanings, the difference lies in the fact that "ought to" is more formal than "should".

  • You should see a doctor if the symptoms persist.(Advice/moderate obligation regarding health.)
  • They ought to be more careful with their spending.(Strong recommendation, close to moral obligation.)

B. lockquote{Should not} and lockquote{ought not to}: Advising Against an Action

These two semi-modals are used to formulate a recommendation to avoid an action.

Concretely, they serve to advise against doing something.

Just like their affirmative forms, ought not to and shouldn't have very close meanings, but ought not to is significantly less common. It is often perceived as slightly dated or excessively formal, and is rarely used today.

  • You shouldn't eat so much sugar.(Advice: it is not recommended to consume that much sugar.)
  • We shouldn't ignore the warning signs.(Strong suggestion: warning signs should not be ignored.)
  • You ought not to be so rude to your parents.(Formal advice: it is not appropriate to be so rude to your parents.)

C. lockquote{Should} / lockquote{ought to} OR lockquote{must} / lockquote{have to}: Which to Prioritize?

Generally, should is used to recommend, and must or have to to impose a strict obligation. Here is a summary:

  • Should / ought to: Used to formulate a light obligation or advice. They suggest an action, but without imperative character.
    • You should drink more water to stay healthy.
  • Must / have to: Used to signal a strong obligation or an imperative necessity, imposed by a law, a regulation, or an urgent situation.
    • You must wear a seatbelt while driving.

7. lockquote{be supposed to}: Expressing Expectation or Moderate Obligation

The phrase "be supposed to" is frequently used to indicate what is expected in a given situation, without necessarily being as binding as "must" or "have to".

  • We are supposed to hand in the report by Friday.(It is expected that we submit the report by Friday.)
  • He is not supposed to park here.(He is not meant to park here; it is forbidden or contrary to regulations.)

8. lockquote{be to}: Formal Obligation in Official Announcements

The phrase "be to" is used in a very formal register or in official announcements, to formulate an obligation or an official schedule.

  • The President is to visit the factory next Monday.(The President must (officially) visit the factory next Monday.)
  • All students are to attend the ceremony.(Students are required to attend the ceremony (formal directive).)

9. Summary and Key Points

On the day of the TOEIC®, mastering these obligation modals is crucial, as they will appear in texts and audio recordings—you will therefore need to understand the context—or directly in fill-in-the-blank exercises.

Summary Table of Modals Expressing Obligation

Must Internal (speaker, moral authority) Strong (subjective) I must finish this task now. Shall Legal authority, directive, or formal commitment Strong (formal or legal) Legal directive: All employees shall comply with the company's code of conduct.Formal commitment: You shall receive the package within 3 days. Have to External (law, rules, circumstances) Strong (objective) Law: I have to pay my taxes by April 15th.Rules: You have to wear a helmet when riding a bike.Circumstances: I have to take an umbrella; it's raining heavily. Need to Internal or external (need) Strong (necessity) Internal: I need to sleep early tonight; I'm exhausted.External: You need to submit the form before the deadline. Should / Ought to Internal (advice, recommendation) Medium (advice, moral) Advice: You should visit the doctor if you feel unwell.Recommendation: We ought to save more money for emergencies. Be supposed to Social norm or expectation Moderate (expected) Norm: Students are supposed to be quiet in the library.Social expectation: You are supposed to RSVP for the wedding invitation. Be to Formal, official framework Strong (in an official context) The Prime Minister is to address the nation tomorrow evening.The students are to meet their teacher at the museum at 10 a.m.

Key Points to Remember About Obligation Modals

Here are the key elements to remember regarding obligation modals:

  1. Must vs. Have to:
  • Must: Strong obligation, subjective, originating from the speaker (or an internal authority).
  • Have to: Strong obligation, but imposed by a regulation or external circumstance.
  1. Shall is used in formal, legal contexts, or for official directives. In everyday English, it is less common and often replaced by must.
  2. The negation of must (mustn't) means "prohibition", whereas the negation of "have to" (don't have to / doesn't have to) means "not obliged to...".
  3. Need to is close to "have to" but emphasizes a personal or practical need more.
  4. Should / Ought to: Advice or attenuated obligation, less binding than "must" or "have to".
  5. Be supposed to: Expresses what is expected or required according to a rule or convention, without being as strict as "must" or "have to".
  6. Be to: A more formal usage, frequent in official and legal contexts, to express a schedule or an obligation.

Other Guides on Modals

To deepen your knowledge of modals, consult our various guides on the subject:

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