Must, Have To, Should: How to Use Them for the TOEIC®

Modal verbs expressing obligation (must, have to, should, ought to) convey different levels of necessity or advice.

They appear very frequently in Parts 5 and 6 of the TOEIC®. You'll find them mostly in professional emails and company policies.

The most common pitfall? Confusing the negative forms of must and have to. They absolutely do not mean the same thing: "You must not" signifies a prohibition, while "You don't have to" expresses a lack of obligation.

The 3 Levels of Obligation in the TOEIC®

Before diving into the details, you need to understand that the TOEIC® distinguishes several degrees of obligation, depending on the source of the constraint and the tone of the message. It is this nuance that is tested on the exam.

Strong Obligation: must vs have to

Both must and have to express a strong obligation, but with an important nuance.
Must comes from the speaker (internal rule, personal conviction).
Have to refers to an external obligation (law, regulation, outside constraint).

You must submit your report before Friday.
(direct order from the manager)
Employees have to wear their ID badges at all times.
(company regulation)

Choosing between must and have to in a specific professional context (formal email, company policy) is one of the classic traps in Part 5.

Lack of Obligation: don't have to

Don't have to means there is no obligation; something is not necessary.

You don't have to attend the meeting if you're busy.
(You are not required to attend the meeting if you are busy.)

Prohibition: must not / mustn't

Must not expresses a strict prohibition. This is a frequent trap on the TOEIC®.

Visitors must not enter the restricted area.
(Visitors are strictly forbidden from entering the restricted area.)

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Typical Business Contexts on the Exam

Obligation modals appear primarily in three types of TOEIC® documents:

Professional Emails: requests, instructions, deadline reminders. Must and have to dominate, especially in formal emails between managers and teams.
Regulations and Policies: dress codes, security procedures, confidentiality rules. Must not and have to come up constantly.
Announcements and Notifications: procedure changes, new requirements. Should for recommendations, must/have to for new binding rules.

The fastest improving candidates consistently spot context keywords (policy, regulation, recommend, optional) before choosing the modal.

The context always provides clues in the surrounding sentences.

The 3 Recurring Traps in Part 5

In Part 5, these modals are rarely tested in isolation. The trick almost always lies in the context of the sentence, which leads many candidates to choose the wrong negative form.

Trap 1: must not ≠ don't have to

The two negative forms have opposite meanings.

You must not use your phone during the presentation.
(forbidden)
You don't have to bring your laptop.
(not necessary)

And here is the classic trap: many candidates choose must not when the context only indicates that an action is not required.
Pay attention to surrounding vocabulary: "optional", "not required", "not necessary" call for don't have to.

Trap 2: have to in the Past and Future Tenses

Have to changes form depending on the tense. Must, however, remains invariable (but is hardly ever used in the past or future).

Yesterday, I had to reschedule the meeting.
(Past marker: 'Yesterday')
Next week, you will have to complete a security check.
(Future marker: 'Next week')

The TOEIC® regularly tests this point in Part 5. If the sentence contains a past time marker (yesterday, last month) or a future marker (next week, soon), have to is almost always the correct answer.

Trap 3: should have + past participle (Regret)

This structure expresses regret or reproach about a past action that was not performed.

You should have informed the client earlier.
(but you didn't)
The report should have been submitted on Monday.
(but it wasn't)

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Ready to Practice?

You have now mastered the nuances between must, have to, and should, along with their negative forms.

These distinctions are tested very frequently in Part 5, and spotting them quickly will earn you valuable points.

On Flow Exam, you can practice directly on the Modals topic in Part 5, using thousands of questions in the exact format of the official TOEIC®.

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