Guide to Prohibition Modals – TOEIC® Preparation

When preparing for the TOEIC®, mastering the expression of what is prohibited or not authorized in a professional environment becomes essential (internal policies, safety standards, instructions to employees, etc.). This guide details the modal structures used to express prohibition in English.

1. “Must not” to Formulate a Formal Prohibition

“Must not” (contracted to “mustn't”) is used to express a categorical and absolute prohibition. This structure emphasizes the imperative necessity to refrain from a given action. In professional contexts, “mustn't” remains the preferred form.

Employees must not share their passwords.(Employees must under no circumstances share their passwords.)
You mustn't leave personal documents on your desk overnight.(You are forbidden from leaving personal files on your desk at the end of the day.)
Visitors must not enter this area without a badge.(Access to this area is strictly prohibited for visitors not carrying a badge.)
Staff mustn't eat in the laboratory.(Staff are forbidden from eating in the laboratory.)

Like all pure modals, “must not” is only conjugated in the present tense. For other grammatical tenses, favor the structures “not allowed to” or “forbidden to.”

Be Careful Not to Confuse with “Do Not Have To”!

It is crucial to distinguish between “must not” and “do not have to,” as these two structures convey radically opposite meanings:

“Must not”: Indicates a strict prohibition. The action is formally forbidden.
- You must not park here.(Parking is prohibited in this spot.)
- You must not talk during the exam.(All communication is prohibited during the test.)
“Do not have to”: Indicates an absence of constraint. The action is not required, but it remains permitted.
- You do not have to park here.(You are not required to park here.)
- You do not have to take notes during the meeting.(Taking notes during the meeting is not an obligation.)

On the day of the TOEIC®, be vigilant about the context of use of these expressions, especially in instructions or dialogues. Terms like “forbidden” or “optional” will help you identify whether it is a prohibition or simply an absence of obligation.

2. “Cannot” to Signify Prohibition

“Cannot” (or its contracted form “can't”) also expresses prohibition, but with a slightly less formal register than “mustn't.” In spoken language and daily exchanges, “can't” is generally preferred over “mustn't.”

You can't use your phone during the meeting.(Phone use is prohibited during the meeting.)
Employees cannot wear jeans on weekdays.(Wearing jeans is forbidden on weekdays for employees.)
You can't park your car in front of the emergency exit.(Parking in front of the emergency exit is prohibited.)
We cannot accept credit cards for this type of payment.(We do not accept credit card payments for this type of transaction.)

Like other pure modals, “cannot” is only used in the present tense. To express prohibition in the past with this structure, use “could not,” and for other tenses, favor “not able to.”

3. “May not” to Express Prohibition Courteously

“May not” allows for the expression of prohibition or refusal of authorization in a diplomatic and official manner. More formal than “cannot” or “must not,” it frequently appears in regulations or directives to indicate that an action is not permitted.

“May not” roughly corresponds to “ne pas être autorisé à” (not being authorized to) in French.

Employees may not leave the office before 5 p.m. without prior approval.(Employees are not authorized to leave the premises before 5 p.m. without prior approval.)
You may not distribute company materials outside the organization.(Distribution of company resources outside the organization is prohibited.)
Staff members may not disclose confidential information to third parties.(Staff members are not authorized to disclose confidential information to external parties.)
Visitors may not take pictures in this facility.(Taking photographs is prohibited for visitors in this establishment.)

Like other pure modals, “may not” is limited to the present tense. To express prohibition with “may not” in other tenses, use “not permitted to” instead.

4. “Not allowed to” and “Not permitted to” to Express Prohibition in All Tenses

Generally, the phrases “not allowed to” or “not permitted to” are used when traditional modals expressing prohibition cannot be used (especially when the sentence is not conjugated in the present tense).

These two structures explicitly express that an action is not authorized or permitted. They are frequently found in official or regulatory contexts.

Tense	Examples
Present	Employees are not allowed to smoke here. (Il est interdit aux employés de fumer ici.) Visitors are not permitted to enter this area. (L'accès à cette zone est interdit aux visiteurs.)
Past	She was not allowed to attend the meeting. (Elle n'était pas autorisée à participer à la réunion.) He was not permitted to access the files. (L'accès aux fichiers lui était interdit.)
Future	You will not be allowed to enter without a badge. (L'entrée vous sera refusée sans badge.) Students will not be permitted to bring food into the library. (Les étudiants ne seront pas autorisés à introduire de la nourriture dans la bibliothèque.)
Present perfect	She has not been allowed to work from home. (Le télétravail ne lui a pas été accordé.) He has not been permitted to share the report. (Il n'a pas reçu l'autorisation de partager le rapport.)

5. “Forbidden to” and “Prohibited to” to Formulate Formal Prohibition

Similar to “not allowed to” or “not permitted to,” you can use “forbidden to” and “prohibited to” to express prohibition in all grammatical tenses.

Nevertheless, these two phrases are extremely formal and appear mainly in regulations, legal, or institutional contexts. They strongly emphasize the notion of prohibition, often associated with potential sanctions.

Employees are forbidden to use the company car for personal trips.(The use of the company car for personal purposes is strictly forbidden to employees.)
You are prohibited from drinking alcohol on these premises.(Drinking alcohol is formally prohibited on these premises.)
Residents are forbidden to play loud music after 10 p.m.(Residents are forbidden from playing loud music after 10 p.m.)
The public is prohibited from entering the restricted zone.(Public access to the restricted zone is prohibited.)

6. “Should not” to Formulate a Warning Close to Prohibition

“Should not” (or “shouldn't”) is not strictly a prohibition modal. It expresses rather a firm recommendation to refrain from an action.

In some contexts, it can be interpreted as an “indirect” prohibition or a strong warning. It is frequently found in safety instructions or professional recommendations.

You should not leave your workstation unlocked.(You should not leave your session open.)
We shouldn't share confidential information via email.(We should not transmit confidential information by email.)
Employees should not send large attachments without compressing them first.(Employees should not send large files without compressing them beforehand.)
You shouldn't wear open-toed shoes in the laboratory.(Wearing open-toed shoes in the laboratory is discouraged.)

Conclusion

To excel at the TOEIC®, mastering the expression of prohibition is essential: instructions, company policies, and safety rules are omnipresent in professional texts and dialogues.

Summary of Modals Expressing Prohibition

Structure	Source of Authority	Level of Formality	Example
Must not	Formal or internal authority (e.g.: company regulation)	Very high (strict prohibition)	Employees must not share their passwords. (Les employés ne doivent pas divulguer leurs mots de passe.)
Cannot	Impossibility or rule (often informal)	High (less formal than must not)	You cannot park here. (Le stationnement est interdit ici.)
May not	Permission refused in an official context	High (very formal and polite)	Visitors may not enter this area without permission. (L'accès à cette zone est interdit aux visiteurs sans autorisation.)
Not allowed to	External or internal authority (e.g.: explicit instructions)	Medium to high	You are not allowed to use your phone during the meeting. (L'utilisation du téléphone est interdite pendant la réunion.)
Not permitted to	Official or legal authority	Very high (formal)	Employees are not permitted to work remotely. (Le télétravail n'est pas autorisé aux employés.)
Forbidden to	Strict prohibition by an official authority	Very high (formal, emphatic)	Residents are forbidden to play loud music after 10 p.m. (Il est interdit aux résidents de diffuser de la musique forte après 22h.)
Prohibited from	Official law or regulation	Very high (formal, legal)	The public is prohibited from entering the restricted zone. (L'accès à la zone restreinte est interdit au public.)
Should not	Advice or warning (often linked to consequences)	Medium (less strict, indirect)	You should not leave your computer unlocked. (Tu ne devrais pas laisser ton ordinateur déverrouillé.)

Key Takeaways on Prohibition Modals

Main Modals for Expressing Prohibition:

Must not conveys a categorical and formal prohibition.
Cannot presents a slightly less formal register and is frequently used in common situations.
May not is extremely formal and suitable for situations where prohibition is communicated courteously or officially.

Alternative Structures:

Not allowed to and Not permitted to are used to express explicit prohibitions, often in a professional or institutional setting.
Forbidden to and Prohibited from emphasize a strict prohibition, often with a legal or regulatory connotation.
Should not suggests a strong recommendation or warning rather than an absolute prohibition.

Compatibility with Grammatical Tenses:

Pure modals (must not, cannot, may not) are used exclusively in the present tense.
Structures like not allowed to or not permitted to allow the expression of prohibition in the past, future, or in other verb tenses (present continuous, past perfect, etc.).

You must adapt your choice based on the context:

Must not and Cannot are perfectly suitable for spoken language or daily situations.
May not, Not permitted to, and Prohibited from are more appropriate for formal or professional contexts.

Mistakes to Avoid:

Never confuse must not (prohibition) with do not have to (absence of obligation).
Modals cannot be conjugated in the past or future; alternative structures like was not allowed to or will not be permitted to must be used.

Other Guides on Modals

Here are our other guides on modals you can consult to prepare for the TOEIC®:

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