LEARN KOREAN (한국어) [GRAMMAR] #1

이다 PAST TENSE

Conjugating 이다 to the past tense is simple, and is done by connecting 이 to 었~. When the last syllable in a word ends in a vowel, 이 + 었 can combine to make 였

Informal Low Respect

Add ~이었어 to all words. If the word ends in a vowel, ~이었어 can contract to ~였어.

나는 바쁜 선생님이었어 - I was a busy teacher
나는 학생이었어 - I was a student
나는 선생님이었어 - I was a teacher

Informal High Respect

This conjugation is the same as above (Informal Low Respect), except for that "~요" is added to the end of ~이었 or ~였. That is, you should add ~이었어요 to all words. If the word ends in a vowel, ~이었어요 can contract to ~였어요.

그것은 큰 비밀이었어요 - That was a big secret
저는 선생님이었어요 - I was a teacher
저는 의사였어요 - I was a doctor

Plain Form

Same as above, but you should add the regular "~다" ending instead of "~어요." That is, you should add ~이었다 to all words. If the word ends in a vowel, ~이었다 can contract to ~였다.

나는 선생님이었다 - I was a teacher
나는 의사였다 - I was a doctor

Formal High Respect

Add ~이었습니다 to all words. If the word ends in a vowel, ~이었습니다 can contract to ~였습니다.

저는 선생님이었습니다 - I was a teacher
저는 의사였습니다 - I was a doctor

In all situations in the past tense, 아니다 is conjugated just like any other word. An example of each respect:

나는 학생이 아니었어
나는 학생이 아니었다
저는 학생이 아니었어요
저는 학생이 아니었습니다

The weird thing is that Korean speakers sometimes would use these:

나는 학생이 아니였어
나는 학생이 아니였다
저는 학생이 아니였어요
저는 학생이 아니였습니다

Just going by the rules of the language, I'd have to assume that the first set is correct. I base this on the fact that in no other word do we add "~였~" to a stem. In other words, "~였~" is created from "이 + 었," but it is never added as a stand-alone thing.