Should
Mustn't
Positive structure
Negative structure
Must
Have to
Shouldn't
Don't have to
Is a weak obligation, and we use it to give advice.
Talks about rules and regulations. The obligation does not come from the person who is speaking.
Modal verb in negative form (shouldn't / mustn't / don't have to) + infinitive form of the action verb
Means you DON'T need to do something, but it's FINE if you want to do it.
Modal verb + infinitive form of the action verb
MILD negative obligation or advice. Expresses that something is a BAD idea.
Expresses that something is ESSENTIAL or MANDATORY from the SPEAKER'S point of view. It is an internal, subjective and strong OBLIGATION that the speaker HIMSELF imposes. Expresses a STRONG obligation that comes from a LAW or REGULATION.
Means it's not ALLOWED. Express PROHIBITION. Means something is FORBIDDEN.