Modal verbs of Obligation Exercises, Examples, Rules

These exercises focus on Modal verbs of Obligation

Modal verbs of obligation show what is necessary, required, or advisable to do. The three main modal verbs of obligation are:

Must – for strong obligation or necessity.
Example: You must wear a helmet when riding a bike.
Have to – also for obligation, often external.
Example: I have to go to work at 9 a.m.
Should – for advice or mild obligation.
Example: You should drink more water.

Illustration of Modal verbs of Obligation

1. Must

Used to show a strong internal or external obligation.
Often used for rules or laws.

Structure:
Subject + must + base verb

Example: You must stop at a red light.

2. Have to

Similar to must but is used for external requirements (e.g., work, school rules).
In the past tense, use had to.

Structure:
Subject + have to + base verb

Example: I have to finish my homework by 8 p.m.
Example (past): Yesterday, I had to visit the doctor.

3. Should

We use should to give advice or a recommendation.
It’s not as strong as must or have to.

Structure:
Subject + should + base verb

Example: You should apologize if you make a mistake.

Common Errors

Common Error	Correct Usage
You must to study for the test.	You must study for the test.
I have finish my project tomorrow.	I have to finish my project tomorrow.
She should goes to the doctor.	She should go to the doctor.

Here are some everyday examples:

At work

Employees must wear an ID badge.
You have to complete the report by Friday.

At home

I have to clean my room before guests arrive.
You should take out the trash.

Health and safety

You must fasten your seatbelt in a car.
You should exercise regularly to stay fit.

Key Differences Between Must, Have to, and Should

Modal Verb	Strength of Obligation	Examples
Must	Strong (rules, laws)	You must not smoke in this building.
Have to	Strong (external requirement)	I have to wake up early for work tomorrow.
Should	Weak (advice, suggestion)	You should try the new restaurant in town.

What is the difference between must and have to?

Must is often used for rules or personal feelings of obligation, while have to refers to external requirements like work or school rules.

Can I use must in the past tense?

No, use had to instead for past obligations. Example: I had to call my teacher yesterday.

Is should a strong obligation?

No, should is used for advice or suggestions, not strong obligations.

What’s the negative form of must?

The negative is must not (or mustn’t), meaning something is prohibited. Example: You must not park here.

Can have to and must be used interchangeably?

Sometimes, but have to is more common in casual speech, while must is often used for formal rules or emphasis.

Modal verbs of Obligation