must and mustn't — rules and prohibitionStating a rule and saying what is not allowed.Related learning areasEnglish GrammarRelated conceptsas … as for saying things are the sameAuxiliary verbs in short answersbe going to — plans and intentionsbe going to — predictions from present evidenceChoosing between present, past, and future verb formsComparative adjectivesComes afterhave to and don't have to — obligation and no obligationQuestionsAll questions in this subjectStart learningStart free practice