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