Both "must" and "should" are model verbs. The term "must" is commonly used to express any unavoidable requirement or obligation. On the other hand, "should" is used as a probability, obligation, advice, recommendation, conditional, and exceptional mood.

Should and must sentence?

It is stronger than should and ought. He must take care of his children. She must mend her ways. You must apologize to her.

Are should and must interchangeable?

Some words can be used interchangeably without changing the meaning of the sentence, but some can be used interchangeably but affect the meaning of the sentence. Should and Must are two similar words that can be used interchangeably in a sentence, but both of them mean different in a sentence.