ESEN
Which one to use?Intermediateverbo modalverbo semi-modal
MustvsHave to
"Must" is internal obligation or logical deduction; "have to" is external obligation imposed by others.
Side-by-side comparison
Must
verbo modalObligation coming from the speaker themselves, or logical deduction about something. Emotionally stronger.
I must call my mother. I have not spoken to her in two weeks.
You must be exhausted after that long trip.
This restaurant must be good, there is always a line outside.
Have to
verbo semi-modalObligation imposed by rules, laws, another person, or circumstances. Neutral and factual.
You have to wear a helmet when riding a motorcycle. It is the law.
She has to work on Saturdays this month. Her boss asked her to.
Do we have to pay in advance, or can we pay at the door?
Common mistake
- •The critical difference is in the negative: "must not" = prohibition.
- •"Don't have to" = not necessary (they are opposites).
- •"You must not smoke" = it is forbidden.
- •"You don't have to smoke" = it is not required (you can choose).
Trick to remember it
- •"Must" positive = internal obligation (I decide it is necessary).
- •"Have to" positive = external obligation (rules impose it).
- •Negative: "must not" = forbidden.
- •"Don't have to" = not required.
Quick rule
"Must" = internal obligation. "Have to" = external obligation. "Must not" = forbidden. "Don't have to" = not required.
Did you know?
MUST has no past tense in modern English, it is a "defective" modal verb (with missing forms). For the past of obligation, HAVE TO in past is always used: "had to." "I had to work late yesterday", never "I musted work late." This makes HAVE TO far more versatile than MUST grammatically: it has a past (had to), future (will have to), present continuous (be having to), perfect (have had to), forms MUST cannot express. This is one of the reasons advanced student textbooks present MUST and HAVE TO together: they are complementary where one ends, the other continues.
Practise what you learned
Exercise 1 · Pick the right one
You _____ try this cake. It's absolutely delicious!
Exercise 2 · Pick the right one
In the UK, you _____ drive on the left. It's the law.
Exercise 3 · Form the word
Related word pairs
LetvsAllow
"Let" is to permit casually or personally; "allow" is to permit formally or with authority.
UnlessvsIf
"Unless" means "if not" or "except if"; "if" is the neutral condition that can be positive or negative.
WhenvsIf
"When" is for certain future events; "if" is for uncertain or hypothetical ones.
AvsAn
'A' is used before consonant sounds; 'an' is used before vowel sounds.
Bryan López
Founder of SpeakUP Academy