"Can"
* Ability in the present: "I can speak Spanish." (You are able to speak Spanish now)
* Possibility: "You can go to the store if you want." (It's possible for you to go)
* Permission: "Can I borrow your phone?" (Asking if it's allowed)
* Requests: "Can you please pass the salt?" (Polite request)
"Could"
* Ability in the past: "I could run a marathon when I was younger." (You were able to run a marathon in the past)
* Possibility in the past: "We could have gone to the beach, but it was raining." (It was possible to go to the beach, but didn't)
* Polite request: "Could you please tell me the time?" (More formal than "Can")
* Conditional: "If I could fly, I would visit every country in the world." (Hypothetical situation)
* Suggestion: "We could go to the movies tonight." (Offering a possibility)
Key Differences
* Time: "Can" is for the present, while "could" can refer to the past or present.
* Formality: "Could" is generally more formal than "can".
* Certainty: "Can" implies more certainty than "could".
Examples:
* Can: I can play the piano. (Present ability)
* Could: I could swim when I was a child. (Past ability)
* Can: Can I have a piece of cake? (Request)
* Could: Could you please pass the salt? (Polite request)
* Could: We could go for a walk later. (Suggestion)
Remember: The specific context will dictate whether "can" or "could" is the appropriate choice.