Must and Have To

Must - Strong Obligation

Internal Obligation (from the speaker)

• I must call my mother. (I feel it’s important)
• We must be more careful. (I think so)
• You must try this cake! (strong recommendation)

Rules and Laws

• Passengers must wear seatbelts.
• You must be 18 to vote.
• All visitors must sign in.

Strong Recommendations

• You must see this movie!
• You must visit Paris someday.
• You must read this book.

Have To - External Obligation

Obligation from Outside

• I have to work tomorrow. (my boss requires it)
• She has to take this medicine. (doctor’s orders)
• We have to pay taxes. (the law says so)

Facts and Circumstances

• You have to be quiet in the library. (library rules)
• Students have to wear uniforms. (school policy)
• I have to leave at 6. (my train is at 6:30)

Must vs. Have To

Note: In everyday American English, “have to” is often used for both.

Past Tense

Must has no past form. Use “had to”:

• Yesterday, I had to work late.
• She had to call the doctor.
• We had to cancel the trip.

Negative Forms - Important Difference!

Must not (prohibition)

• You mustn’t smoke here. (it’s forbidden)
• You mustn’t tell anyone. (don’t do it)
• We mustn’t be late. (it’s not allowed)

Don’t have to (no obligation)

• You don’t have to come. (it’s not necessary, but you can)
• She doesn’t have to work today. (she’s free, no obligation)
• We don’t have to decide now. (we can wait)

Comparison

Quiz