Can vs. Could

Attribute	Can	Could
Past Ability	Cannot talk	Could not talk
Possibility	Can happen	Could happen
Politeness	Can you help me?	Could you help me?
Permission	Can I go?	Could I go?

Definition

Can and could are both modal verbs in English that are used to express ability, possibility, permission, or requests. Can is the present tense form of the verb, while could is the past tense form. Both words are commonly used in everyday conversation and writing, but they have slightly different meanings and uses.

Ability

When talking about ability, can is used to express present ability or capability. For example, "I can speak Spanish fluently" indicates that the speaker currently has the ability to speak Spanish. On the other hand, could is used to express past ability or a hypothetical ability. For example, "When I was younger, I could run faster" indicates that the speaker had the ability to run faster in the past.

Possibility

Can is used to express present possibility or likelihood. For example, "It can rain later today" indicates that there is a possibility of rain in the future. Could, on the other hand, is used to express past possibility or a hypothetical situation. For example, "It could have been a mistake" indicates that there was a possibility of it being a mistake in the past.

Permission

When talking about permission, can is used to ask for or give permission in the present. For example, "Can I go to the bathroom?" is a question asking for permission to go to the bathroom. Could, however, is used to ask for or give permission in a more polite or formal way. For example, "Could I borrow your pen, please?" is a more polite way of asking for permission to borrow a pen.

Requests

Both can and could can be used to make requests, but there is a slight difference in tone. Can is used for more direct or informal requests. For example, "Can you pass me the salt?" is a direct request for someone to pass the salt. Could, on the other hand, is used for more polite or formal requests. For example, "Could you please help me with this?" is a polite way of asking for help.

Summary

In summary, can and could are both modal verbs that are used to express ability, possibility, permission, and requests in English. Can is used for present ability, possibility, permission, and requests, while could is used for past ability, possibility, permission, and requests. Understanding the subtle differences between can and could can help you communicate more effectively in various situations.