If you’ve already read the lesson on 있다 and 없다, you’ll be able to make sense of this lesson a bit more quickly. To recap, 있다 has to do with the presence of something, and 없다 has to do with the absence of something. Keep that in mind as we look at the following two constructions:
-ㄹ 수 있다 / -을 수 있다 = to be able to do X
-ㄹ 수 없다 / -을 수 없다 = to not be able to do X
The only differences between these two constructions are the 있다 and 없다. So we can see that 수 있다 means to have 수, or for 수 to be present, and 수 없다 means for it to be absent. So what is 수?
수 is something special called a “bound noun”. All that means is that it is a noun that has no meaning on its own, it needs to be used together with something else. But our bound noun, 수, must mean something like “the ability to do something”. Then if you use it with 있다 it means you have that ability, and if you use it with 없다 it means you don’t. In simpler terms, it means you “can” or you “can’t” do something.
How to attach it:
These grammatical constructions can be attached to verbs and adjectives, and they both follow the same rule. They attach to the root of the word. Remember that every verb and adjective in Korean ends in 다 in its dictionary form. Slice off the 다 and you have the root.
When attaching these grammatical constructions to a word that ends in a vowel, use -ㄹ 수 있다 or -ㄹ 수 없다. That means you attach that ㄹ right onto the last syllable of the root.
The Truth Untold
너에게 다가설 수 없으니까 ~ “because I can’t draw near to you”
Original verb: 다가서다 – to go up to, to approach
When attaching these grammatical constructions to a word that ends in a consonant, use -을 수 있다 or -을 수 없다.
이젠 웃을 수 있고 ~ “I can smile now, and…”
Original verb: 웃다 – to laugh, to smile
Intro: Boy Meets Evil
참을 수 없는 내 욕심 ~ “My greed that I can’t suppress”
Original verb: 참다 – to suppress, to control
One more note:
There is another grammatical construction in Korean that translates to “can’t” in English, but the meaning is different. That construction is: -지 못 하다.
-ㄹ/-을 수 없다 means that you can’t do something because you don’t have the ability to do it. Like, “I can’t swim” because I have not learned to swim. Or “I can’t see” because I’m visually impaired.
-지 못 하다 means that you can’t do something, not because of inability, but because something is preventing you from doing it. Like “I can’t see” because something is blocking my view. Or “I can’t study” because I’m too distracted, or I don’t have time, not because I am incapable of studying.