must

Modal Verbs of Deduction – Must/Can’t/May (not) & Might (not)

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In English, there are several modal verbs of deduction. They allow us to guess if something is true based on the information available. Four very important ones to know are must, can’t, may (not), and might (not).[1]https://learnenglish.britishcouncil.org/grammar/intermediate-to-upper-intermediate/modals-deductions-about-the-present

modal verbs of deduction

Must

You use the word “must” when you are 100% (or nearly) positive that something is true.[2]https://smitkit10-11.weebly.com/deduction.html

For example:

  • You must be tired after that workout. (I am very sure that you are tired)
  • I don’t have my phone. It must be on my desk. (I am sure that the phone is on my desk)
  • She must study for the test if she wants to do well. (I am very sure that if she wants to pass the test it is required that she study)

May (not) & Might (not)

You use the words “may (not)” or “might (not)” if you are 50% sure of a fact.

For example:

  • They are not here yet. They might be stuck in track. (I am not exactly sure why they aren’t here)
  • Frank may be able to help us with the problem. (There is a 50% chance that Frank can help)
  • The airline told us that the flight might be delayed due to weather. (There is a 50% chance that the flight gets delayed due to weather)

Difference between Might and May

May is used for situations that could be factual or could be possible.

Might is used for speculative situations that didn’t actually happen.[3]https://writingexplained.org/may-vs-might-difference

Can’t

You use the word “can’t” when you are 100% (or nearly) sure that something is false.[4]https://www.test-english.com/explanation/b1/modal-verbs-deduction-must-might-cant/

For example:

  • Sorry, I can’t do that. It’s against the law. (I am 100% unable to do the task)
  • You can’t stay in the house while they paint it. The fumes are toxic. (You are 100% not allowed to be in the house)
  • I can’t drive today. I just had an eye test and can’t see. (Due to the eye test, I am 100% unable to drive)

Example Exercises

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Question 1 of 8

1. Why did they give him the promotion over her? He has only been here a month! He _____ know more than her about how the company works.

Question 1 of 8

Question 2 of 8

2. Do you know where my wallet is? It _____ be in the house because I remember paying for lunch today.

Question 2 of 8

Question 3 of 8

3. You seem too know a lot about that subject. You _____ really enjoy reading about it.

Question 3 of 8

Question 4 of 8

4. I have been extremely tired at work lately. I _____ be working too hard.

Question 4 of 8

Question 5 of 8

5. That is an expensive gift! Your fiancée _____ be rich!

Question 5 of 8

Question 6 of 8

6. It _____ rain tomorrow.

Question 6 of 8

Question 7 of 8

7. I _____ not be able to make the party. I think my boss is going to make me stay late at work.

Question 7 of 8

Question 8 of 8

8. You _____ be a great student. You are always getting good grades.

Question 8 of 8


 

References[+]

Modals – Must vs. Have to

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The modals “must” and “have to” talk about obligation.[1]https://www.englishclub.com/grammar/verbs-modals-have-to-must-not.htm The difference between the two types of obligation is if it internal or external.

must

Must

In general, you use “must” to talk about personal opinion. This is subjective. That means, the speaker thinks it is necessary.

must

For example:

  • I must study; otherwise, I won’t do well on the test.

(The implication is that the speaker wants to do well on the test. Therefore, they are going to study. It is not a requirement for them to study.)

  • You must try this sandwich! It is so tasty!

(The implication is that you really should try the sandwich that I think is very tasty. However, if you don’t want to, you are required to.)

  • If I am going to become a professional basketball player, I must practice every day.

(The implication is that it is necessary to practice every day in order to become a professional basketball player. However, neither becoming a professional basketball player nor practicing every day is a requirement.)

Have to

In general, you use “have to” to talk about external rules or opinions. In other words, you use it when rules and other people are telling you to do something. It is not a personal opinion.

have to

For example:

  • In England, you have to drive on the left hand size of the road.

(The implication is that it is the law in England to drive on the left hand side of the road.)

  • I have to wear a uniform at work.

(The implication is that it a requirement to wear a uniform at work.)

  • You have to wait for the stop light to turn green before you can move forward.

(It is the law that you can’t drive through a red light. You must wait for the green light to drive.)

Practice Exercises

Please go to Modals – Must vs. Have to to view this quiz

References[+]