Might be or Must be? what does they mean? And wich is the difference between them?
Qué significan? y Cuál es la diferencia entre ellas?

Question

Answer

Might be = Es posible que pueda ser
Must be = Debe ser

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must -- more certainty

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"What do they mean?"

Use "must be" when you are absolutely certain, and "might be" when you think so, but you are not really sure.

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I'll try to give you some examples:

might --> possibility

maybe it'll work ; it's possible that it works ; it "might" work

must --> need to / have to

you need to clean your room ; you have to clean your room ; you "must" clean your room

must --> guess

She won first place:
I bet she's happy ; I guess she's happy ; She "must" be happy