Let’s have a look at the differences:
SHOULD is used to:
- give advice or a suggestion: You should drink more water.
- make a recommendation: You should try that new cafe I went to last night!
- to talk about right or wrong: This should be the way to do it.
Negative form: shouldn’t
Some more examples:
- He should be punctual.
- Riya shouldn’t go alone.
- They shouldn’t travel by train.
MUST is used to:
- express certainty: This must be the shop!
- express necessity: All students must wear their white uniform tomorrow.
- express strong recommendation: You must try this new recipe!
Negative form: mustn’t : used to prohibit someone from doing something. But as it is quite severe, it’s not used much.
Some more examples:
- You mustn’t play in the sand.
- Sheila must be here somewhere.
- You mustn’t argue with your elders.