Can and could: ability, permission and requests

Use can to describe a skill or something a person is able to do. Put can after the subject, then use the base verb: the simple form found in a dictionary, such as drive, speak or help. Can stays the same with I, he, she and plural subjects.

Keep both verbs unchanged in this pattern. After can, use speak rather than speaks or to speak. Ability can mean a learned skill, but it can also depend on the situation, such as being close enough to hear music. The sentence tells you which meaning fits.

Use can't or cannot when someone is not able to do something. Can't is the short form; cannot is normally written as one word. Both can describe a missing skill or a temporary problem. The words around them show whether the difficulty is general or just happening now.

Do not add don't or doesn't before can. The negative belongs to can itself, and the following verb still uses its base form. Yet can show that a skill may develop later; right now can make a temporary limit clear.

To ask a usual yes-or-no question, put can before the subject, followed by the base verb. Do not add do or does. A question word such as what or where comes before can when you need more information.

A short answer can use a subject with can or can't, without repeating the action. Match the subject to the person you mean: a question addressed to you usually receives an answer with I. When you ask about someone else, the reply can use he, she or they.

Use could for a general ability in the past, often with a time phrase such as when I was younger. Could not and couldn't describe a past inability. Could follows the same form rules as can: no -s, no to before the next verb, and no did in ordinary questions.

A past skill is different from one successful action. To report that you succeeded on one particular occasion, was able to or managed to is usually clearer. Could remains common for past seeing or hearing and for a general skill. Couldn't can describe either a general difficulty or one unsuccessful occasion.

Use can I or can we to ask permission for an action you want to do. The question concerns whether the action is allowed. You already know how to do it, but another person controls the choice, owns the item or knows the rules.

Could I and could we also ask permission now. Could makes the request less direct and often sounds more polite. It does not place the action in the past. Please and a friendly tone can help with either form.

Use can to give someone permission now. This is true even when the question began with could I. An answer with can clearly allows the action. You can also use a natural reply such as yes, of course, when the permission is clear.

Use can't or cannot when an action is not allowed. A short reason can make a refusal easier to understand. The same negative forms also express inability, so use the situation to decide: a locked door may prevent entry, while a visitor rule may forbid it.

Use can you or could you with a base verb when you want another person to act. In a request, the important meaning is that you want help. You are usually not testing whether the person has the physical skill to perform the action.

Could you is a useful way to make a request less direct, especially with someone you do not know well. Can you is also normal in everyday requests. To accept, a reply such as sure or of course is often enough; you do not need to answer a present request with I could.

Use could to suggest something for someone to consider. With we could, you put forward a possible shared plan. With you could, you offer an idea to another person. The suggestion leaves room for a different choice.

A suggestion with could can refer to now or the future. Add a time phrase when it helps. Can can also present an available option, but could is useful when you want to put an idea forward without treating it as an agreed plan.

Could can mean that something is possible but not certain. A speaker may be guessing where an object is or what will happen. A time word and the surrounding information help distinguish this use from a past ability or a suggestion.

Can often describes what is possible in general, including something that happens sometimes. Could can describe one uncertain possibility now or later. Avoid deciding from the modal alone: first ask whether the sentence describes a skill, permission, a request, a suggestion or a guess.