Must vs. Have To

B1 · IntermediateModal Verbs

Must and have to both express obligation, but only one of them can form a past tense, a future tense, and a question with do.

What you'll learn

  • Must is a frozen modal: one form only, no -s, no past tense, no infinitive
  • Have to behaves like a regular verb: has/have, had to, will have to, do/does
  • Had to is the past tense for both must and have to
  • Will have to is the future form, since must has none

Two ways to express obligation

Must and have to both say that something is necessary or required. The real difference between them isn't meaning — it's grammar.

"I must finish this by Friday."
"She has to finish her homework before dinner."

Must never changes form

Must has exactly one form, in every person and number, with no -s, no infinitive (to must doesn't exist), and critically, no past tense form of its own.

"He has to catch an early train tomorrow. (not 'he musts')"
"Yesterday, I had to work late. (not 'I musted')"

Have to fills the gaps

Because must can't change form, have to takes over wherever a different tense or a question with do is needed — the past, the future, and questions.

"We had to show ID at the old office."
"We will have to reschedule the meeting."
"Did you have to wait long?"

Real English

"We had to cancel the trip."
"They will have to submit new documents."
"Did she have to retake the exam?"
"He has to leave early today."

Watch out

✗I musts finish this by Friday.
✓I must finish this by Friday.

Must never takes -s, even with he/she/it — it has exactly one form.

✗Yesterday, I musted work late.
✓Yesterday, I had to work late.

Must has no past tense form — use had to instead.

✗We will must reschedule the meeting.
✓We will have to reschedule the meeting.

Must can't follow will — use have to for the future instead.

Real life — Talking about a busy week

"You look exhausted — what happened?"

"I had to work late every night this week."

"That sounds rough. Will you have to do the same next week?"

"I hope not — I must get some rest this weekend."

Practice

Exercise 1 · Choose the correct sentence

Choose the correct sentence.

Exercise 2 · Choose the correct sentence

Choose the correct sentence — past obligation.

Exercise 3 · Choose the correct sentence

Choose the correct sentence.

Exercise 4 · Choose the correct question

Choose the correct question.

Exercise 5 · Choose the correct answer

Which modal has no past tense form of its own?

Exercise 6 · Choose the correct sentence

Choose the correct sentence for a rule that existed only in the past.

Exercise 7 · Choose the correct sentence

Choose the correct sentence.

Exercise 8 · Choose the correct sentence

Choose the correct sentence — future obligation.

Exercise 9 · Complete the sentence

Complete (past obligation): 'Last year, I ___ (have to) travel a lot for work.'

Exercise 10 · Complete the sentence

Complete (future obligation): 'After the merger, employees ___ (have to) reapply for their jobs.'

Exercise 11 · Sort into groups

must finish
had to finish
will have to finish
has to finish
must attend
had to attend

0 / 6 sorted

Quick challenge

Five quick questions to check what stuck.

Question 1 / 5

Score: 0/0

Choose the correct sentence.

You learned

  • Must has exactly one form — no -s, no infinitive, no past tense.
  • Have to behaves like a regular verb, so it can form any tense.
  • Had to is the past tense for both must and have to.
  • Will have to is the future form, since must has none.

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