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Equality (이다) and Existence (있다/없다)

Let's talk about why the English word "is" is disgusting. It's used in three different, unrelated capacities:

  1. "The cat is soft" applies the adjective "soft" to the noun "cat".
  2. "I am a cat" is an equality between myself and the cat.
  3. "There is a cat" asserts the existence of a cat.

This is an ugly overloading of a single word with many unrelated functions. To make things worse, it has several completely arbitrary forms: "is", "am", "are", "was", "were" are actually all just different forms of "to be".

Korean does things better and separates these three cases cleanly:

  1. In Korean, adjectives behave like verbs, so no additional word is needed: "고양이가 폭신해요" (cat soft) is a perfect sentence.
  2. For equality, there's a special word 이다, and a special negation 아니다.
  3. For existence, there's a special word 있다, and a special opposite 없다 ("there does not exist").

And that's it! Okay, fine, there is a bit more.

Equality (이다)

이다 seems to be neither a verb nor an adjective, but in a special class by itself. To use 이다, you just attach it directly to the end of the second noun. So "X is Y" becomes "X가 Y이다", roughly speaking. There's no space added after Y.

However, the present-tense conjugation has some arbitrary rules. In contrast, the past-tense conjugation is what one would predict if one pretended 이다 was a normal verb.

Level Cons + 이다 (present) Vowel + 이다 (present) Cons + 이다 (past) Vowel + 이다 (past)
Diary -이다 -이다 or -다 -이었다 -였다
Casual -이야 -야 -이었어 -였어
Polite -이에요 -예요 -이었어요 -였어요
Formal -입니다 -입니다 or -ㅂ니다 -이었습니다 -였습니다

Example

  • 난 고양이다 = I am a cat. [diary]
  • 난 고양이야 = I am a cat. [casual]
  • 저는 고양이예요 = I am a cat. [polite]
  • 저는 고양이입니다 = I am a cat. [formal]

Non-equality (아니다)

The opposite of 이다 is 아니다, "is not". Unlike 이다, it does require a space, and the noun before it takes the subject marker 이/가.1 So "X is not Y" becomes "X는 Y가 아니다".

Level Present Past
Diary 아니다 아니었다
Casual 아니야 아니었어
Polite 아니에요 아니었어요
Formal 아닙니다 아니었습니다

Example

  • 난 고양이가 아니다 = I am not a cat. [diary]
  • 난 고양이가 아니야 = I am not a cat. [casual]
  • 저는 고양이가 아니에요 = I am not a cat. [polite]
  • 저는 고양이가 아닙니다 = I am not a cat. [formal]

Warning

Notice the polite present tense conjugation is 아니에요 and NOT 아니예요. This is counter-intuitive because 고양이예요 has 예. (Apparently this even trips up native speakers?)

Existence (있다/없다)

You can treat 있다 and 없다 as adjectives for conjugation.

Example

  • 고양이가 있다 = There is a cat. [diary]
  • 고양이가 있어 = There is a cat. [casual]
  • 고양이가 있어요 = There is a cat. [polite]
  • 고양이가 있습니다 = There is a cat. [formal]

Depending on context, these could also mean "I have a cat". Similarly:

Example

  • 고양이가 없다 = I do not have a cat. [diary]
  • 고양이가 없어 = I do not have a cat. [casual]
  • 고양이가 없어요 = I do not have a cat. [polite]
  • 고양이가 없습니다 = I do not have a cat. [formal]

  1. Technically, this noun isn't a second subject. Korean school grammar calls this kind of 이/가 word a complement (보어). There are only two words in Korean that use complements this way: 아니다 and 되다 ("to become"), as in 물이 얼음이 돼요 = Water becomes ice. ↩