Must vs She oughta be fine

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

Must

High-frequency chunkA1

She oughta be fine

InformalTop 2,000 (common)
Most formal: MustMost common: Must
 MustShe oughta be fine
Pronunciation🇬🇧 /["/məst//mʌst/","/ˈmʌsnt/"]/🇺🇸 /["/məst//mʌst/","/ˈmʌsnt/"]/🇬🇧 //ˈɔːtə bə faɪn//🇺🇸 //ˈɔːtə bə faɪn//
MeaningSomething that is necessary or very important.She should be okay.
ExampleYou must finish your homework before playing outside.After the meal, she oughta be fine for the rest of the day.
RegisterNeutralInformal
How commonHigh-frequency chunkTop 2,000 (common)
CEFR levelA1-
Collocationsmust see, must do, must have, must rememberoughta be fine, oughta do, oughta go, oughta know
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.Using 'oughta' in formal contexts where 'ought to' is more appropriate., Confusing 'oughta' with similar-sounding phrases like 'ought not to'.
Usage notesUse 'must' when giving strong advice or making strong recommendations. Avoid using it in casual conversations where 'should' might be more appropriate.Used informally to express belief or expectation about someone's state or situation. Appropriate in casual conversation, but not in formal writing.

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Must
She oughta be fine

Frequently asked questions: Must vs She oughta be fine

What's the difference between Must and She oughta be fine?

Must: Something that is necessary or very important. She oughta be fine: She should be okay.

Which is more formal: Must and She oughta be fine?

Must is the most formal of these.

Which is more common: Must and She oughta be fine?

Must is the most common in everyday English.

Can you show an example of each?

Must: You must finish your homework before playing outside. She oughta be fine: After the meal, she oughta be fine for the rest of the day.

Can I use Must and She oughta be fine interchangeably?

Not always. Must and She oughta be fine 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.

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