A fairly basic grammar pattern in Korean is the (으)ㄹ 수 있다 pattern that expresses the ability or possibility of a verb. Some sources I found do specifiy that descriptive verbs can be used but are light on actual examples. So anyway, while going through TTMIK’s Half in Korean & Half in English, lesson 3, I came across a curious use of the pattern:
현우: 아무튼, 아재 개그 저는 정말 좋아해요. 이게 똑똑해야 할 수 있거든요.
Cassie: That’s right. You’ve got to be very smart. We’re the only smart ones in the office, right?
My confusion stems from my brain translating the sentence partway into English and wondering why it was used in conjunction with the pattern expressing a necessity with 해야 하다:
- (Original) 이게 똑똑해야 할 수 있거든요 For this, you have to [be able to] be clever
- 이개 똑똑해야 하거든요 For this, you have to be clever
So the second sentence is an edit by me which should have the exact same meaning. I also find expressing the first sentence literally in English sounds awkward: You do not possess the ability to be clever, either you are clever in a situation or you are not. So my question is, in practicle terms, is the addition of 수 necessary/more natural, and why?