Negative expressions in Korean are a bit peculiar compared to Western languages. One of the most peculiar ways negation works is what you can call word negation. This happens when instead of using the regular negation methods in Korean grammar, you need to use particular verbs like 아니다, 없다 and 모르다.
Word Negation: 아니다
The first form of word negation is the first most Korean language learners tend to learn: 아니다. 아니다 is the negative copula verb in Korean and thus the antonym of the copula verb 이다. When negating 이다 in Korean, you have to use this negative copula verb instead of regular methods such as -지 않다 or 안.
The negative copula 아니다 indicates that the topic of the is not something. To do so, it is common practice that you use the subject marker 이/가 with whatever the topic is not. Keep this in mind.
가: 민수 씨는 학생이에요?
나: 아니요, 학생이 아니에요. 선생님이에요.
A: Is Minsu a student?
B: No, he isn’t a student. He is a teacher.
Word Negation: 없다
The second form of word negation is perhaps the second form of negation you’ve learned in Korean: 없다. As you then remember it is the negative form of the verb 있다 and like 아니다, you have to use 없다 instead of using the regular negation methods. This is a very important one to remember because you will use it extensively due to its presence in plenty of Korean grammar like -(으)ㄴ 적이 없다, -(으)ㄹ 수 없다, -기가 이를 데 없다, etc.
The negative 없다 indicates that something is not present in a certain location or that something is not in the possession of someone. As with 있다, the object nor present is marked commonly by the subject marker 이/가.
가: 책이 책상 위에 있어요?
나: 아니요, 책이 없어요.
A: Is the book on the desk?
B: No, the book is not.
Word Negation: 모르다
The last form of word negation in Korean is 모르다. This is the negation of the Korean verb 알다 (to know, to understand). Like all other forms you, therefore, cannot use 알다 with regular negation forms in Korean like -지 않다 and 안. Like 있다, it is important to really know this negation as it is part of many Korean grammar topics like -(으)ㄹ 줄 모르다, -(으)ㄴ/는 불 몰랐다, -(으)ㄹ지도 모르다, etc.
The negative 모르다 indicates that you either don’t know something or you don’t understand something. The thing you don’t know or understand is marked by the object particle -(으)ㄹ/를.
가: 이 노래의 가수를 아나요?
나: 아니요, 몰라요.
A: Do you know the singer of this song?
B: No, I don’t know.