The document discusses the use of "must" and "have to/has to" to express obligation or necessity. "Must" is used when the speaker feels something is necessary or to express a wish. "Have to" is used when an external situation makes something necessary, such as a doctor's orders, rules, or requests from others. Both "must" and "have to" are used with different verb forms depending on tense, negation, or questions.

1. Obligation Must & Have to

2. Obligation We use must and have to/has to to say that something is necessary. You'll be leaving college soon. You must think about your future. When we use the past, or the future with will, we need a form of have to. For negatives and questions with have to/has to and had to, we use a form of do. I don't have to work on Sundays. Why does Andrew have to study every evening?

3. Obligation We use must when the speaker feels that something is necessary . You must exercise. (I'm telling you.) We must be quiet. (I'm telling you.) Must can also express a wish. I must buy a newspaper. I want to see the racing results. We use have to when the situation makes something necessary. I have to exercise. (The doctor told me.) We have to be quiet. (That's the rule.) I have to buy a newspaper. The boss asked me to get one. We have to invite Trevor and Laura. They invited us last time.