Must vs Have to Exercises

Must and have to both express obligation, but they come from different sources. Use must when the obligation comes from the speaker — a personal rule, strong recommendation, or internal feeling: "I must remember to call her" (I am telling myself). Use have to when the obligation comes from outside — rules, laws, or someone else's authority: "I have to wear a uniform at work" (my employer requires it).

The negative forms are very different and often confuse learners: mustn't means "it is prohibited" — you are not allowed to do it: "You must not smoke here." Don't have to means "it is not necessary" — you can do it if you want, but it is not required: "You don't have to come if you're busy." This difference between prohibition (mustn't) and lack of obligation (don't have to) is one of the most tested grammar points in English exams. Another key difference: "must" has no past form, so we use "had to" for past obligation: "I had to work late yesterday."