Answered By: Writing Center Last Updated: Apr 20, 2015 Views: 1
You can use must, mustn't, needn't following the format: subject + must/mustn't/needn't + infinitive.
Use must for actions that have to be done: We must leave now if we want to catch that flight.
Use mustn't for actions that should not be done: You mustn't go there. It is a dangerous place to be in.
Use needn't for actions that do not need to be done but one can still do it if he/she really wants to: We needn't go since there are already so many who volunteered.
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