Expressing Necessity and Obligation in English

Today, we’re going to learn how to express necessity and obligation in English. These are important concepts because in everyday life, we often need to talk about things we must do, should do, or need to do, whether for personal reasons, according to rules, or due to external expectations.

By the end of this lesson, you'll know how to use various modal verbs and phrases to talk about things that are required, recommended, or unnecessary. This knowledge will help you communicate more effectively in both casual and formal situations. Let’s dive in!

learn: Adverbs of frequency

1- Key Modal Verbs and Expressions for Necessity and Obligation:

1. Must

Usage: "Must" expresses a strong obligation or necessity, often from the speaker’s perspective or from an external source like rules or laws.
Example:

"You must wear a seatbelt when driving." (Law)
"I must finish this report by tomorrow." (Personal necessity)

2. Have to

Usage: "Have to" is similar to "must" in meaning, but it is often used to express external obligations or necessity, things that are required by outside circumstances.
Example:

"I have to work late tonight." (External necessity, perhaps a work requirement)
"You have to show ID to enter the club." (Rule/requirement)

3. Ought to

Usage: "Ought to" suggests a recommendation or moral obligation, weaker than "must" or "have to." It expresses what is morally right or advisable.
Example:

"We ought to help those in need." (Moral obligation)

4. Should

Usage: "Should" expresses advice, suggestions, or weak obligation. It’s often used to indicate something is the right or expected thing to do but not necessarily required by rules.
Example:

"You should study for your exams." (Advice)
"He should go to the doctor." (Recommendation)

5. Need to

Usage: "Need to" implies necessity, particularly for things that must be done for practical or survival reasons.
Example:

"I need to get some sleep." (Necessity)
"She needs to finish her homework before going out." (Requirement)

6. Don’t have to / Don’t need to

Usage: These negative forms indicate the lack of necessity or obligation.
Example:

"You don’t have to bring anything to the party." (No obligation)

7. It’s (not) necessary to / It’s (not) required to

Usage: These expressions are often used in formal contexts, especially when referring to external obligations or requirements.
Example:

"It’s necessary to wear safety gear when working in the lab." (Formal necessity)
"It’s not required to RSVP for the event." (Lack of requirement)

8. Be supposed to

Usage: This phrase indicates an expectation or something that is generally required by social norms or rules, but it may not be as strict as "must" or "have to."
Example:

"You’re supposed to arrive on time." (Expectation)

9. Required to

Usage: This is more formal and is typically used in legal or professional contexts.
Example:

"All employees are required to attend the meeting." (Legal or professional requirement)
"You are required to submit the form before Friday." (Official obligation)

2- Types of Obligation and Necessity:

1. External Necessity: When something is required by external factors such as rules, laws, or social expectations.

"You must wear a mask in this store." (Law or store policy)
"Students have to submit their assignments by Friday." (School rule)

2. Internal Necessity: When something is needed for personal reasons, like health or efficiency.

"I need to take a break." (Personal need)

3. Advice and Recommendations: Suggestions on what is a good idea to do.

"You should eat more vegetables." (Health advice)
"He ought to take a vacation soon." (Recommendation)

4. Moral Obligation: When something is required by social norms or ethics.

"You should help others whenever you can." (Moral duty)
"People ought to respect their elders." (Moral guideline)

5. Lack of Necessity: When something is not required or necessary.

"You don’t have to come to the meeting if you’re busy." (No obligation)
"She doesn’t need to worry about the project right now." (No necessity)

Important Notes:

Must vs. Have to: "Must" is more personal, while "have to" often reflects external circumstances. In many contexts, they are interchangeable.

Example:

"I must study for my physics exam." (Personal necessity)
"I have to study for the my physics exam." (External requirement)

Should vs. Ought to: "Should" is more commonly used in modern English, while "ought to" is somewhat formal or old-fashioned.

Example:

"You should go to the gym more often."
"You ought to go to the gym more often."

Tasks

Task 1: complete with the correct adverb of frequency :

1. You _______ bring your textbook tomorrow. (must / should / don’t have to)

2. She _______ go to the meeting because she has another appointment. (must / doesn’t have to / should)

3. I _______ finish this project by Friday for my boss. (have to / ought to / don’t need to)

4. You _______ wear a helmet when riding a bike in this area. (must / should / need to)

5. We _______ help the people who are in need. (ought to / don’t have to / must)

Correction of task 1:

must
doesn’t have to
have to
must
ought to

Task 2: Complete with Use must, have to, should, ought to, need to, don’t have to, or shouldn't .

Sentence	Verb choice	Explanation
She _______ bring her passport to the airport.	has to	Requirement for travel
You _______ tell the teacher if you are going to be late.	should	Strong suggestion or advice
We _______ go to the meeting, but it would be helpful.	should	Suggestion or recommendation
He _______ work on the weekend, but he wants to.	doesn’t have to	Personal choice or preference
She _______ worry about the test; it’s not that hard.	doesn’t have to	No necessity or obligation

Recapitulation of the lesson

Great job today, everyone! We’ve covered several ways to express necessity and obligation in English . Keep practicing these structures in your conversations and writing to feel more confident expressing obligations in English.