ㄹ 수 있다

can, be able to

The everyday way to say can: attach it to a verb and it covers both ability and possibility. 쓸 수 있다 "you can use it", 갈 수 있을까요? "can they make it there?", 어떻게 유지할 수 있었냐고요? "how was I able to keep it up?". Swap 있다 for 없다 and it becomes cannot (할 수 없어요). After a consonant it appears as 을 수 있다. It is built from a noun meaning way or means, which is why 수 stands as a separate word with spaces around it.