Can vs. Could: What's the Difference?
Quick Answer
"Can" expresses present ability, permission, or possibility (I can swim; can I leave early?). "Could" expresses past general ability (I could swim when I was five), a more polite or tentative present request (could you help me?), or a hypothetical possibility (I could go, but I'm not sure). "Could" is more indirect and softer than "can" in almost every use.
Difference at a Glance
| Feature | Can | Could |
|---|---|---|
| Time reference | Present / general truth | Past general ability, or present hypothetical |
| Requests / permission | Direct, casual ("Can I sit here?") | More polite, indirect ("Could I sit here?") |
| Specific past achievement | Not used for this | Not used alone — use "was/were able to" or "managed to" |
| Example | She can speak three languages. | She could speak French even as a child. |
Definitions
Can
Present ability, permission, or general possibility.
can + base verb
"He can play the guitar."
"Can I open the window?"
"Traffic can be terrible here."
Could
Past general ability, polite requests, or hypothetical possibility.
could + base verb
"I could read before I started school."
"Could you pass the salt, please?"
"We could go to the beach this weekend."
Grammar Rule
Key Rule: Use "can" for present ability, permission, or possibility. Use "could" for general ability in the past, for softer and more polite requests in the present, and for hypothetical or uncertain possibilities.
Important exception: for a single, specific past achievement (not a general ability), avoid "could" and use "was/were able to" or "managed to" instead — for example, "After years of practice, she was able to finish the marathon," not "she could finish the marathon."
Common Mistakes
Incorrect: Despite the flat tire, he could arrive on time.
Correct: Despite the flat tire, he was able to arrive on time.
A single, specific past success should use "was able to", not "could".
Incorrect: Can you please to close the door?
Correct: Could you please close the door?
Modal verbs like "could" are followed directly by the base verb, with no "to".
Incorrect: When I was a child, I can climb trees easily.
Correct: When I was a child, I could climb trees easily.
General ability in the past needs "could", not "can".
More Correct Examples
Mini Quiz
1. Choose the more polite request: "_____ you open the window, please?"
2. Choose the correct word: "As a teenager, she _____ run five kilometers without stopping."
3. Fix the sentence: "After months of training, he could finally run a marathon."
Common Learner Questions
Why can't I use "could" for a specific past success?
In standard English, "could" describes a general capacity that existed over a period of time, not a single completed event. For one specific success (passing a test, winning a race, escaping danger), native speakers use "was/were able to" or "managed to" instead.
Is "could" always more polite than "can"?
In requests, yes — "could" sounds softer and more indirect than "can", which is why it's common in polite or formal situations, such as speaking to a stranger, a customer, or a superior.
Can "could" refer to the future?
Yes, "could" often expresses a present or future possibility that is uncertain or hypothetical, as in "We could go camping next month if the weather is nice" — this is not about the past at all.