can 1 
(kăn; kən when unstressed)
(kăn; kən when unstressed)aux.v. past tense could (kd)
1.
a. Used to indicate physical or mental ability: I can carry both suitcases. Can you remember the war?
b. Used to indicate possession of a specified power, right, or privilege: The president can veto congressional bills.
c. Used to indicate possession of a specified capability or skill: I can tune the harpsichord as well as play it.
2.
a. Used to indicate possibility or probability: I wonder if my long lost neighbor can still be alive. Such things can and do happen.
b. Used to indicate that which is permitted, as by conscience or feelings: One can hardly blame you for being upset.
c. Used to indicate probability or possibility under the specified circumstances: They can hardly have intended to do that.
3. Usage Problem Used to request or grant permission: Can I be excused?
[Middle English, first and third person sing. present tense of connen, to know how, from Old English cunnan; see gnō- in the Appendix of Indo-European roots.]
Usage Note: Generations of grammarians and teachers have insisted that can should be used only to express the capacity to do something, and that may must be used to express permission. But children do not use can to ask permission out of a desire to be stubbornly perverse. They have learned it as an idiomatic expression from adults: After you clean your room, you can go outside and play. As part of the spoken language, this use of can is perfectly acceptable. This is especially true for negative questions, such as Can't I have the car tonight? probably because using mayn't instead of can't sounds unnatural. While the distinction between can and may still has its adherents in formal usage, the number appears to be falling. In our 2009 survey, 37 percent of the Usage Panel rejected can instead of may in the sentence Can I take another week to submit the application? But more than half of these said can was only "somewhat (rather than completely) unacceptable" in this use, and the overall percentage of disapproval fell from more than 50 percent in an earlier survey. · The heightened formality of may sometimes highlights the speaker's role in giving permission. You may leave the room when you are finished implies that permission is given by the speaker. You can leave the room when you are finished implies that permission is part of a rule or policy rather than a decision on the speaker's part. For this reason, may sees considerable use in official announcements: Students may pick up the application forms tomorrow. · Like may, can is also used to indicate what is possible: It may rain this afternoon. Bone spurs can be very painful. In this use, both can and may often have personal subjects: You may see him at the concert. Even an experienced driver can get lost in this town.