Be (~be, is)

In English, "to be" is a linking verb that connects a subject to its identity or description: "I am a teacher," "She is tall." Korean works the same way, but English speakers often miss the crucial difference: Korean treats identity statements as fundamentally different from other actions. The verb 이다 doesn't describe an action—it defines what something IS.

Here's the key insight: English blurs the line between "I am" (identity) and "I am running" (action). Korean keeps them completely separate. 이다 is exclusively for identity, state, and classification. When you say "나는 학생이다" (I am a student), you're literally saying the noun "student" IS the identity of "I." There's no auxiliary verb hiding behind it; the entire meaning lives in 이다 alone.

The structure is deceptively simple because Korean doesn't use a separate copula like English does—there's no hidden "I is". Instead, the subject noun directly combines with 이다. Notice also: English adds articles ("a," "the"), but Korean 이다 never does. "나는 학생이다" is "I am a student," but literally: "I [topic] student + is." The bare noun + 이다 is the complete thought.

Finally, formality levels matter: 이다 is raw/informal (dictionary form), -다 is a written/reported form, and 입니다 is the polite formal you'll hear in daily speech. These aren't interchangeable—they signal social context and register. English "I am a teacher" doesn't change based on politeness, but Korean does: "선생님이에요" (polite) vs. "선생님이다" (blunt). This grammaticalization of respect is a major 한국어 mindset difference.