To be compelled to in order to fulfill some need or achieve an aim: When youre taking kayaking lessons, a lifejacket is a must. Must is a modal verb. You use must not or mustnt to … You use must to indicate that you think it is very important or necessary for something to happen. It is followed by the base form of a verb. In this sense, must does not form a negative. How to use must in a sentence. The meaning of must is be commanded or requested to. We must hurry if were to arrive on time. You must pay your dues. To be forced to, as by convention or the requirements of honesty: If used with a negative infinitive it indicates obligatory … We usually use must to talk about obligations which come from the speaker and we generally use have (got) to when we refer to obligations that come from outside the speaker. Must is a modal verb that expresses necessity, obligation, or strong recommendation. Used as an auxiliary to express obligation or compulsion: I must say, that is a … A must is something thats so important it cant be missed or ignored.