Learn Hardcore Korean: i jibeun keoyo.

은 is the topic marker you attach to a noun that ends in a consonant. It’s like saying “as for …” in English. Here, 이 집은 means “as for this house,” introducing it as the topic of your sentence.

Why is 은 used instead of 는 after 집?

The topic particle comes in two forms: 은 after a consonant-ending noun and 는 after a vowel-ending noun. Since 집 ends with the consonant ㅂ, we use 은. If you had a noun like 나무 (tree), it would be 나무는.

What’s the difference between the topic marker 은/는 and the subject marker 이/가?

은/는 (topic) frames what the sentence is about, often implying contrast or known information.
이/가 (subject) marks the subject performing an action or possessing a quality, often introducing new information.
In practice, 이 집은 커요 (“As for this house, it’s big”) presents the house as known or contrasted with something else, whereas 이 집이 커요 more neutrally states “This house is big,” perhaps answering “Which one is big?”

Why isn’t there a separate verb for “is” in 이 집은 커요?

In Korean, descriptive verbs (often called adjectives in English) double as predicates. 크다 is the dictionary form meaning “to be big.” When you conjugate it into polite present tense, it becomes 커요. You don’t need an extra “to be” verb like English uses.

What level of politeness or formality is 커요?

커요 is in the polite informal style (called 해요체). It’s appropriate for everyday conversation with people you’re not extremely close to but still wish to speak politely to.

Could I say 이 집이 커요 instead of 이 집은 커요?

Yes, it’s grammatically correct. Using 이/가 (as in 이 집이 커요) simply emphasizes the subject “this house” without the contrast or topic nuance that 은/는 brings. Both mean “This house is big,” but 은 often implies you’re saying that about the house specifically (maybe compared to another), whereas 이 집이 feels more like a straightforward identification.

How would I turn 이 집은 커요 into a question: “Is this house big?”

You can keep the same words and rely on rising intonation:
이 집은 커요?
Or use the formal question ending -까 for more formality:
이 집은 클까요?

Both are perfectly natural ways to ask if the house is big.