Must vs They should

When to use each in English, with meaning, register, and examples.

Must

High-frequency chunkA1

They should

Top 1,000 (very common)
 MustThey should
Pronunciation🇬🇧 /["/məst//mʌst/","/ˈmʌsnt/"]/🇺🇸 /["/məst//mʌst/","/ˈmʌsnt/"]/🇬🇧 //ðeɪ ʃʊd//🇺🇸 //ðeɪ ʃʊd//
MeaningSomething that is necessary or very important.A phrase suggesting that something is necessary or advisable for a group of people.
ExampleYou must finish your homework before playing outside.They should finish their homework before playing outside.
RegisterNeutralNeutral
How commonHigh-frequency chunkTop 1,000 (very common)
CEFR levelA1-
Collocationsmust see, must do, must have, must rememberthey should know, they should try, they should consider, they should agree, they should remember
Antonymscan, may, might-
Common mistakesUsing 'must' in situations where 'have to' is more suitable., Confusing 'must' with 'might' or 'may', which imply possibility instead of necessity., Using 'must' with the gerund form instead of the base form of the verb.Confused with 'they shouldn't' for negative advice., Using 'should' without a main verb (e.g., 'They should go')., Incorrectly placing 'should' outside of the verb phrase.
Usage notesUse 'must' when giving strong advice or making strong recommendations. Avoid using it in casual conversations where 'should' might be more appropriate.Used to express advice or recommendations. It's appropriate in most contexts, including formal discussions. Avoid using it in overly casual speech.

See it in real clips

Must
They should

Frequently asked questions: Must vs They should

What's the difference between Must and They should?

Must: Something that is necessary or very important. They should: A phrase suggesting that something is necessary or advisable for a group of people.

Can you show an example of each?

Must: You must finish your homework before playing outside. They should: They should finish their homework before playing outside.

Can I use Must and They should interchangeably?

Not always. Must and They should are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.

Related comparisons