Learn the correct use of Must/ Ought to/ Need

Use of MUST

Must expresses

a) Necessity
b) Obligation
c) Determination
d) Compulsion
e) Possibility
f) Expectation
g) Prohibition
h) Certainty or Belief
i) Emphatic Advice

Let us try to understand each use through examples:

a) To express necessity

1. You must run fast to win the race.
2. You must work hard to secure a good rank.

b) To express obligation

1. Army must follow the protocol.
2. Children must look after their ageing parents.

c) To express determination

1. I must take a leave today.
2. I must try to solve this.
3. I must see the doctor today.

d) To express compulsion

1. We must follow the traffic rules.
2. You must not bully other children.

e) Certainty or Belief

1. She must have fought with her friends.
2. She must have got the coffee bag for me.
3. He must be the leader of the team.

f) To express emphatic advice

1. You must practice for your matches regularly.
2. We must serve our mother land.
3. Tobacco is injurious to health! You must give it up.

g) To express possibility

1. He must have received the parcel by now.
2. The coach must have finished his instructions by now.
3. The mother must have fed the baby by this time.

h) To express expectations

1. There must be a bug in the software.
2. She must have a good plan for the party.

i) To express prohibition

1. You must not enter the hall without entry passes.
2. Children must not touch my office bag.
3. You must not go to sleep without brushing your teeth.

j) Necessity or Obligation in Future Tense

1. Students must finish the homework by tomorrow.
2. He must score well in this set.
3. We must conserve forests for a better tomorrow.

Use of OUGHT + TO

Ought + to is used to express:

a) Moral Duty or Social Obligation in present tense
b) Advice
c) Strong Probability.

a) To express moral duty or social obligation in Present Tense


1. You ought to respect your parents.
2. We ought to serve our nation.
3. You ought to work for your country.
4. You ought to listen to your teachers.

b) To advice

1. You ought to hire a good coach.
2. You ought to read to your children every night.
3. We ought to hurry up as we are late for the train.
4. You ought to work hard to crack the entrance exam.

d) To express strong probability of something

1. She is a very hard-working girl; she ought to get through the entrance exam.
2. He is a very good actor; he ought to win a national award.

Below are some of the examples of wrong usage of “ought to”. Also provided is the right way to say/ write those sentences.

a.) The charges are serious; you should consult a good lawyer. – Incorrect
     The charges are serious; you ought to consult a good lawyer. – Correct

b.) A teacher should do everything to make a pupil learn. - Incorrect
     A teacher ought to do everything to make his pupil learn. - Correct

c.) One must serve the motherland. – Incorrect
     One ought to serve the motherland. - Correct

Use of NEED

Need can be used as
  • a principal verb and
  • a defective verb.
1. When used as a principal verb, it means “to be in need of something/ someone.”


1. I need your help.
2. The child needs mother’s help.
3. The child does not need mother’s help.
4. Does the child need mother’s help?
5. Child needed mother’s help.

2. When used as a defective verb, it is used in negative and interrogative sentences.

i) In negative and interrogative sentences, need is used to express weakness, necessity or obligation.
ii) Here it is used only in the present tense.


1. I need not be a party to it.
2. You need not get into the details.
3. Need he join them?
4. Need I come to your house?

Following are some of the common mistakes in the usage of “need”. Also provided is the right way to speak/write each of the sentences.

a.) He should not run, we’re not late.
     He need not run, we’re not late.

b.) You should not get into the kitchen. Children are doing a fantastic job.
     You need not get into the kitchen. Children are doing a fantastic job.

c.) You may not follow it up personally, just ask someone to call.
     You need not follow it up personally, just ask someone to call.