Modals, Definitions and Example Sentences; English Modals of NECESSITY, Definitions and Examples Need (verb) (without to) is used in negative and interrogative sentences. Also, we can use don`t have to / doesn`t have to / didn`t have to(past), must for the same purpose. In the affirmative, we use need to to express necessity. Example Sentences He mustn’t be late for the meeting. I must be careful not to upset her. They must leave immediately. You don’t have to give me money but I can if you want. You need to do the exercises, they are obligatory. You had to try