1can 
/kən, ˈkæn/ verb
past tense could /kən, ˈkæn/ verb /kəd, ˈkʊd/; present tense for both singular and plural can; negative can·not /ˈkænɑt, kəˈnɑ:t, Brit ˈkænət/ or can't /ˈkænt, Brit ˈkɑ:nt/ [modal verb] 1 : to be able to (do something)
▪ I don't need any help. I can do it myself. ▪ I can't decide what to do. ▪ All we can do [=the only thing we can do] now is wait. : to know how to (do something) ▪ She can read, can't she? ▪ I can whistle. : to have the power or skill to (do something) ▪ A weight lifter can lift a very heavy weight. ▪ She can play the piano. ▪ Only Congress can do that. : to be designed to (do something) ▪ a car that can hold five people [=a car that has enough room for five people] ▪ How fast can [=does, will] the car go? — sometimes used without a following verb ▪ I visit her whenever I can. ▪ I don't know if I'll be able to fix the problem, but I'll do what I can. ▪ Please help us if you can. 2 — used to describe what someone sees, feels, thinks, etc. ▪ “Can you see him yet?” “Yes, I can see him clearly.” ▪ I can barely hear you. ▪ Can [=do] you remember/understand how to do it? 3 a — used to say that something is or is not possible ▪ Do you think he can still be alive? [=do you think it is possible that he is still alive?] ▪ I don't think he can still be alive. [=I think he must be dead] ▪ These problems can be dealt with more easily at the local level. ▪ You can't always get what you want in life. ▪ At this time of year many birds can be found on the island. [=there are many birds on the island at this time of year] ▪ If you don't tell me what the problem is, I can't help you. ▪ You can't be very smart [=you aren't very smart] if you believe that! ▪ He was supposed to be here an hour ago. Where can he (possibly) be? [=where is he?] — sometimes used in the emphatic phrase as…as can be ▪ I want a cake as big as can be! [=I want the biggest cake possible] ▪ They seemed as happy as can be [=they seemed extremely happy] when I last saw them.
b — used in speech to express surprise or disbelief ▪ You must be joking! You can't/cannot (possibly) be serious! ▪ He can't really have meant that. [=I don't believe that he meant that] ▪ You can't (possibly) believe that! ▪ The price is $50? That can't be right. [=that must be wrong] 4 a : to have permission to (do something)
▪ You can do it tomorrow if you like. ▪ “Can I leave now?” “No, you can't.” ▪ You can't leave until you finish washing the dishes. — compare may 4
b — used in speech to make a request or suggestion ▪ Can [=could] I have another cookie? ▪ Can [=could] you open the window a little more, please? ▪ You can sit here if you like. ▪ If you're not sure what to do, you can always ask for help. ▪ We can leave early if you're feeling tired. — compare may 3 5 a — used to say what should or should not be done ▪ You can't leave now! The party is just getting started! ▪ Why can't you be more polite? [=you should be more polite; why aren't you more polite?]
b — used in angry speech to tell someone to do something ▪ If you don't like it here, you can just leave! 6 a — used to describe the way a person sometimes behaves ▪ She can be very rude at times. [=she is sometimes very rude]
b — used to describe something that sometimes or often happens ▪ In this part of the country the weather can change quickly. [=the weather often changes quickly]
▪ I don't need any help. I can do it myself. ▪ I can't decide what to do. ▪ All we can do [=the only thing we can do] now is wait. : to know how to (do something) ▪ She can read, can't she? ▪ I can whistle. : to have the power or skill to (do something) ▪ A weight lifter can lift a very heavy weight. ▪ She can play the piano. ▪ Only Congress can do that. : to be designed to (do something) ▪ a car that can hold five people [=a car that has enough room for five people] ▪ How fast can [=does, will] the car go? — sometimes used without a following verb ▪ I visit her whenever I can. ▪ I don't know if I'll be able to fix the problem, but I'll do what I can. ▪ Please help us if you can.
b — used in speech to express surprise or disbelief ▪ You must be joking! You can't/cannot (possibly) be serious! ▪ He can't really have meant that. [=I don't believe that he meant that] ▪ You can't (possibly) believe that! ▪ The price is $50? That can't be right. [=that must be wrong]
▪ You can do it tomorrow if you like. ▪ “Can I leave now?” “No, you can't.” ▪ You can't leave until you finish washing the dishes. — compare may 4
b — used in speech to make a request or suggestion ▪ Can [=could] I have another cookie? ▪ Can [=could] you open the window a little more, please? ▪ You can sit here if you like. ▪ If you're not sure what to do, you can always ask for help. ▪ We can leave early if you're feeling tired. — compare may 3
b — used in angry speech to tell someone to do something ▪ If you don't like it here, you can just leave!
b — used to describe something that sometimes or often happens ▪ In this part of the country the weather can change quickly. [=the weather often changes quickly]
usage Could is used as the past tense of can to describe an ability that someone had in the past or to say that something was possible in the past.
▪ I could run fast when I was young, but I can't run fast now. ▪ It used to be that you could drive for miles here without seeing another person, but now there are houses and people everywhere. To describe a specific occurrence in the past, use was/were able to instead of could. ▪ By working long hours, we were able to finish the project on time. In the future tense, will be able to is used. ▪ If you keep practicing, you'll be able to play the piano someday. ▪ She believes that someday people will be able to vote at home on their computers. Can can be used to suggest something that might happen in the future. ▪ If we save enough money, we can go to Hawaii for our vacation next year.
▪ I could run fast when I was young, but I can't run fast now. ▪ It used to be that you could drive for miles here without seeing another person, but now there are houses and people everywhere. To describe a specific occurrence in the past, use was/were able to instead of could. ▪ By working long hours, we were able to finish the project on time. In the future tense, will be able to is used. ▪ If you keep practicing, you'll be able to play the piano someday. ▪ She believes that someday people will be able to vote at home on their computers. Can can be used to suggest something that might happen in the future. ▪ If we save enough money, we can go to Hawaii for our vacation next year.
no can do
informal + humorous — used in speech to say that you cannot do something that you have been asked or told to do ▪ “Can you give me a ride to work tomorrow?” “Sorry—no can do. My car is in the shop.”
— compare 3can
