Copula 이다/아니다 in Korean

Overview

The copula 이다 (to be) and its negative 아니다 (to not be) are essential CEFR A1 structures for equating nouns: "A is B" or "A is not B." Unlike English "is/am/are," 이다 attaches directly to the noun it follows, functioning almost like a particle. It is used exclusively with nouns — for adjective descriptions, use descriptive verbs instead.

이다 conjugates differently from regular verbs, with special polite forms 이에요 (after consonants) and 예요 (after vowels). The formal form is 입니다. The negative 아니다 is a standalone verb meaning "to not be" and conjugates regularly.

These structures appear in virtually every Korean conversation, from self-introductions to identifying objects. Mastering them is one of the first steps in forming complete Korean sentences.

How It Works

이다 (to be) — Polite Level

Noun ending	Form	Example
Consonant	noun + 이에요	학생이에요 (is a student)
Vowel	noun + 예요	의사예요 (is a doctor)

이다 — Formal Level

Noun ending	Form	Example
Consonant	noun + 입니다	학생입니다
Vowel	noun + 입니다	의사입니다

아니다 (to not be)

Level	Form	Example
Polite	아니에요	학생이 아니에요 (not a student)
Formal	아닙니다	학생이 아닙니다

Note: The noun before 아니다 takes the subject particle 이/가.

Examples in Context

Korean	Romanization	English	Note
학생이에요.	hak-saeng-i-e-yo	(I) am a student.	consonant + 이에요
의사예요.	ui-sa-ye-yo	(He) is a doctor.	vowel + 예요
한국 사람이 아니에요.	han-guk sa-ra-mi a-ni-e-yo	(I) am not Korean.	negative
이것은 책입니다.	i-geo-seun chae-gim-ni-da	This is a book.	formal
뭐예요?	mwo-ye-yo	What is it?	question
선생님이에요.	seon-saeng-ni-mi-e-yo	(She) is a teacher.	occupation
커피가 아니에요. 차예요.	keo-pi-ga a-ni-e-yo. cha-ye-yo	It's not coffee. It's tea.	negative + positive
제 친구예요.	je chin-gu-ye-yo	(This is) my friend.	introduction
오늘이 월요일이에요?	o-neu-ri wor-yo-i-ri-e-yo	Is today Monday?	question

Common Mistakes

Using 이에요 after vowel-ending nouns

• Wrong: 의사이에요
• Right: 의사예요
• Why: After vowels, 이 contracts with 에 to become 예요. This contraction is mandatory in speech.

Using 이다 for adjective meanings

• Wrong: 크다이에요 (trying to say "is big")
• Right: 커요 (just conjugate the descriptive verb)
• Why: 이다 is only for noun equations (A = B). Descriptions use descriptive verbs directly.

Forgetting 이/가 before 아니다

• Wrong: 학생 아니에요
• Right: 학생이 아니에요
• Why: The noun being negated takes the subject particle 이/가 before 아니다.

Usage Notes

이다 is unique in Korean grammar — it behaves partly like a verb (it conjugates) and partly like a particle (it attaches directly to nouns). In casual speech, 이다 becomes 이야 (after consonants) or 야 (after vowels): 학생이야, 의사야. The formal 입니다 is used for the most polished speech and is standard in broadcasts, presentations, and written announcements.

Practice Tips

• Practice self-introductions: 저는 [name]이에요/예요. [nationality] 사람이에요. [occupation]이에요/예요.
• Create "this is / this is not" pairs: 이것은 책이에요. 그것은 책이 아니에요. 펜이에요.
• Notice how 이에요/예요 and 입니다 appear in Korean signs, announcements, and menus.

Related Concepts

• Prerequisite: Polite Ending -아/어요 — understanding speech levels helps contextualize 이다's forms