Usage of can and could

"Can" expresses present ability, general possibility, permission, and informal requests, while "could" indicates past ability, polite requests, uncertain possibility, and hypothetical or conditional situations. "Could" is considered more polite and formal than "can" in requests and offers.

Use "Can" for:

Present Ability: Something you are currently able to do or know how to do.

Example: "She can play the piano".

General Possibility: What is possible in general, but not necessarily in a specific future event.

Example: "It can rain in April".

Permission: Asking for or giving permission.

Example: "Can I go outside?".

Informal Requests/Offers: To ask someone to do something in a friendly way, or to offer help.

Example: "Can you open the window?".

Use "Could" for:

Past Ability: Something you were able to do in the past.

Example: "He could run fast when he was young".

Polite Requests: More formal and polite than "can".

Example: "Could you open the window, please?".

Uncertain or Hypothetical Possibility: When something is possible but not certain, or in a conditional situation.

Example: "It could rain later".

Suggestions: To suggest an idea or course of action.

Example: "You could wear your pink suit".

Key Differences

Formality: "Could" is more polite and formal than "can".

Tense: "Can" is generally used for the present, while "could" is often used for the past.

Certainty: "Can" can indicate a higher likelihood of possibility, whereas "could" suggests a lower or uncertain possibility.