Modal Verbs of Prohibition

Exercises

Explanation

The three main modal verbs of prohibition are:

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

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

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

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

We use must not to show a very firm rule or something that is forbidden.

Examples:

• You must not touch the hot pan.

• Children must not run near the pool.

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

We use cannot to show a rule or restriction that stops someone from doing something.

Examples:

• You can’t park in front of the gate.

• Visitors cannot use this elevator.

3. May not – formal or polite prohibition

We use may not in official or formal situations when we want to sound polite.

Examples:

• You may not enter the office without a badge.

• Students may not use the printer after 6 p.m.

Basic Structure

Subject + modal verb + base verb

Correct: You must not eat in the lab.
Incorrect: You must not to eat in the lab.

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

Examples in Everyday Life

At school:

• Students must not share test answers.

• You cannot leave the class without permission.

• Guests may not use the teacher’s computers.

At work:

• Staff must not remove office equipment.

• You cannot enter the server room.

• Employees may not print personal documents.

In public places:

• You must not feed the animals in the zoo.

• You cannot swim here; it’s dangerous.

• Passengers may not stand near the driver.

Quick Tips

• must not = very strong rule

• cannot = general restriction

• may not = formal “not allowed”

• should not = advice, not prohibition