The Meanings and Uses of Must, Need to and Have to
The modal verb must is used with a bare infinitive to express the idea that something is necessary or obligatory or that something is certain or probable. Need to and have to also express the idea of being necessary or obligatory. The past tense of must is must, but it is used only in reported speech or in certain senses of the word. Had to is often used as the past tense of must. There are more details in the sections below.