Might vs. Must

'Might' and 'must' are modal verbs that confuse learners as they both talk about possibilities. In this lesson, we will learn more about them.

What Is Their Main Difference?

The main difference between modal verbs 'might' and 'must' is that 'might' talks about permission and 'must' talks about obligations.

'Might' is a modal verb mainly used to show possibilities and to give advice. 'Might' is considered as the past tense of 'may' but it can be used in the present and the future tense. Take a look at the following example:

You might think he is innocent but he is not.

They might be on their way.

'Must' is a modal verb that is mainly used to show that something is a necessity. It is also used to talk about likely events and suggestions. For example:

She must be tired.

You must come home before 9 p.m.

Similarities

Talking about Possibilities

'Might' and 'must' are used to show possibilities and probabilities. 'Must' talks about a great chance of occurrence, while 'might' talks about a lesser chance of occurrence. For instance:

He might be on his way.

He must be on his way.

Negation and Question

Modal verbs are used to make negative or interrogative sentences.
To make negative sentences, we add 'not' to the modal verb as illustrated below:

Might → Might not → Mightn't
Must → Must not → Mustn't

Look at the examples below to see the negation process:

I might report them to the police. → I might not report them to the police.

I must fulfill my duties. → I must not fulfill my duties.

To create interrogative form, we invert the modal verb with the subject:

They might be after the girl. → Might they be after the girl?

He must be loud. → Must he be loud?

With Other Modals

We use only one modal verb in a sentence. We cannot use modal verbs with other modal verbs. Take a look at these incorrect sentences:

I ~~might~~ ~~can~~ give him a lift.

I ~~must~~ ~~shall~~ wake up sooner.

Differences

Talking about Necessities

We use 'must' to talk about actions or events that need to be done. The occurrence of these events is a necessity and at times a duty. For instance:

You must look after your brothers.

All citizens must stay at home until further notice.

Giving Advice

We often use 'might' to politely give advice or a fair warning. In this case, we often pair 'might' with 'want' as the main verb. Take a look at the following examples:

You might want to lower the volume.

You might want to stop crying.

Giving Suggestions

'Might' is used to make a suggestion about a future possibility. For instance:

You might try adding a bit more sugar next time.

You might try not yelling at him.

With Conditionals

'May' and 'must' can be used as conditional verbs. In the table below, you can see an overview of 'might' and 'must' with all conditional types:

	Might	Must
Conditional Type 1	✓	✓
Conditional Type 2	✓	✗
Conditional Type 3	✓	✗
Zero Conditional	✗	✗

Conditional Type 1

'Might' and 'must' are used in conditional type 1. In this type, we show a condition and its results. These conditions are real situations with a high chance of occurrence. For instance:

If you run everyday, you might get thinner.

If you run everyday, you must get thinner.

Conditional Type 2

This type of conditionals is used to talk about hypothetical situations in the present or future. These situations are imaginary and they have a low chance of occurrence. We use 'might' in this conditional. We cannot use 'must' in this type since it indicates certainty which cannot be applied to hypothetical situations. Take a look at the following example:

If I take a couple of weeks off, I might feel better.

If I finish this task, I might be able to go home sooner.

Conditional Type 3

Conditional type 3 talks about an imaginary past that could happen but never did. We often use it to express lost causes and what-ifs. We use 'might' in this type of conditional. 'Must' cannot be used in this conditional. For example:

You might have been accepted if you had studied harder.

I might have won the competition if the judges weren't corrupt.

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