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'Can' expresses ability or possibility in the present; 'could' expresses past ability or hypothetical possibility.
Side-by-side comparison
"Can" expresses what you are able to do now or what is possible now. It also works for asking permission in a direct way.
She can speak four languages, her family moved a lot when she was young.
Can you help me carry these bags upstairs? They are too heavy for me alone.
You can borrow my umbrella if you need it. I am staying inside all afternoon.
"Could" is the past of "can" and its conditional form. Use it for past abilities, hypothetical possibilities, or more polite requests.
When she was young, she could run a kilometre in under four minutes, she was very fast.
Could you pass me the salt, please? This soup needs a little more flavour.
He could not come to the party because he had a bad cold and a high fever.
Common mistake
- •Using "can" in formal work emails sounds informal.
- •"Can you please review my proposal?" is correct but casual; in professional contexts use "could": "Could you please review my proposal?".
- •And "she could finish the project on time" is ambiguous for a specific achievement: use "managed to finish" to make clear she succeeded.
Trick to remember it
- •Formality scale for requests: "Would you mind...?" (most formal) > "Could you...?" (formal) > "Can you...?" (informal).
- •In work emails, always "could"; with friends, "can" is natural.
Quick rule
- •"Can" = present ability, informal request.
- •"Could" = past ability, theoretical possibility, formal or polite request.
Did you know?
In British workplace English, a manager who says "Can you do this?" can sound close to giving an order, while "Could you do this?" acknowledges that the request is a small imposition. The modal you pick often signals politeness and hierarchy as much as ability.
Practise what you learned
Exercise 1 · Pick the right one
When she was young, she _____ run a kilometre in under five minutes.
Exercise 2 · Pick the right one
"_____ you help me carry this box? It's really heavy."
Exercise 3 · Form the word
Related word pairs
"Can" expresses ability or capacity (to be able to do something); "may" expresses formal permission or possibility (something might happen).
'Going to' expresses a prior plan or evidence-based prediction; 'will' expresses a spontaneous decision or general prediction.
'Should' and 'ought to' express advice or moral obligation with virtually the same meaning; 'should' is more common.
'A' is used before consonant sounds; 'an' is used before vowel sounds.
Bryan López
Founder of SpeakUP Academy