When do you use 'must' for strong obligation / rule?

Example: "All PRs must pass CI before merging — no exceptions."

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Modal verb

must

Q: When do you use 'must' for logical deduction?

Example: "Every test is failing at the same line — the build must be broken."

must + base verb (no 's', no 'to')

Uses

Strong obligation / rule

“All PRs must pass CI before merging — no exceptions.”

Logical deduction

“Every test is failing at the same line — the build must be broken.”

Common mistakes

✕“You must to update your branch.”

✓“You must update your branch.”

✕“This function musts return a string.”

✓“This function must return a string.”

Choose the correct modal

Pick the modal that fits the meaning of each sentence.

All PRs pass CI before merging — no exceptions.

Every test is failing at the same line — the build be broken.

Spot the correctly formed sentence

Only one option follows the rules for modal verbs. Pick it.

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Written by

Roxana Lafuente

Lingua-e's founder

Roxana Lafuente is a software engineer with 8+ years of experience. At the beginning of her career, even though she had already passed the First Certificate in English, she still froze every time she had to speak up in the daily standup. That was a gap nobody was fixing. After 2,000+ standups, she figured out what actually builds fluency: practice that looks like your real work. She built Lingua-e so other developers wouldn't have to take the long road to feel confident working in an international development environment.