Modal Verbs of Prohibition

Exercises

Explanation

The three most common modal verbs used to show prohibition are:

• must not (mustn’t) – a strict and strong rule

• cannot (can’t) – a general restriction or something that is not possible

• may not – a formal or polite way to say “not allowed”

Each of these forms communicates a different level of seriousness or formality.

1. Must not (mustn’t) – strong prohibition

Must not is used when something is strictly forbidden. This form communicates urgency and is often used in safety rules, warnings, or clear instructions.

Examples:

• You must not lean over the balcony railing.

• Visitors must not touch the museum displays.

This modal expresses a rule that must be followed without exception.

2. Cannot (can’t) – not allowed or not possible

Cannot (can’t) is used for general restrictions. It shows that the situation or the rules make the action impossible or not permitted.

Examples:

• You can’t enter the staff room without permission.

• Passengers cannot board the train once the doors are closed.

This form sounds slightly less strict than must not, but it clearly communicates that the action is not allowed.

3. May not – formal or polite prohibition

May not is used in more official or polite contexts. It is common in written rules, notices, or situations where we want to sound respectful.

Examples:

• You may not use the conference room without reserving it first.

• Children may not play in this area after sunset.

This modal is often found in regulations, signs, or professional communication.

Basic Structure

The structure of all modal verbs of prohibition is:

Subject + modal verb + base verb

Examples:

Correct: You must not enter this room.
Incorrect: You must not to enter this room.

Modal verbs are always followed by the base form of the verb (without to).

Prohibition in Everyday Situations

Modal verbs of prohibition appear in many real-life contexts. Here are some typical examples:

At school:

• Students must not destroy school property.

• You cannot use the hallway during class time.

• Parents may not enter the classroom during lessons.

At work:

• Employees must not share confidential documents.

• You cannot delete files from this computer.

• Staff may not eat at their desks during client hours.

In public places:

• You must not light fires in the park.

• Cyclists cannot ride here; it’s a pedestrian zone.

• Visitors may not bring pets into the building.

Quick Tips to Remember

• must not = a very strict rule (strong prohibition)

• cannot (can’t) = general restriction or impossibility

• may not = formal or polite “not allowed”

• should not = advice, not prohibition