When do you use 'could' for present possibility (less certain than 'can')?

Example: "The outage could be caused by the new deployment."

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Modal verb

could

Q: When do you use 'could' for past ability / past general possibility?

Example: "Before we added the cache, one bad query could bring down the whole site."

Q: When do you use 'could' for polite request?

Example: "Could you take a look at this stack trace when you have a minute?"

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

Uses

Past ability / past general possibility

“Before we added the cache, one bad query could bring down the whole site.”

Polite request

“Could you take a look at this stack trace when you have a minute?”

Present possibility (less certain than 'can')

“The outage could be caused by the new deployment.”

Common mistakes

✕“She couldn't to access the server.”

✓“She couldn't access the server.”

✕“He could reviews the code.”

✓“He could review the code.”

Choose the correct modal

Pick the modal that fits the meaning of each sentence.

you take a look at this stack trace when you have a minute?

Back when we had only one server, a single bad query bring down the entire site.

Spot the correctly formed sentence

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

Previous: can Next modal: may

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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.