Learn Hardcore Korean: gajogi jibe isseoyo.

이 is the subject‐marking particle attached to nouns ending in a consonant. It tells us that 가족 (“family”) is the subject of the sentence—i.e. the thing whose existence or location is being stated. (If the noun ended in a vowel, you’d use 가 instead.)

Why is it 집에 and not 집에서?

The particle 에 marks a static location (“at home”). By contrast, 에서 often indicates the place where an action happens (“doing something at home”) or the origin (“from home”). Since we’re simply stating “family is located at home,” 에 is the correct choice.

What does 있어요 mean in this context?

Here, 있어요 is the polite present tense of the verb 있다, meaning “to exist” or “to be located.” So 집에 있어요 means “(they) are at home.” Note that 있다 can also mean “to have” when used with a possessor, but this is the existential use.

How polite is the ending –요 in 있어요?

The –요 ending marks the informal polite (also called “standard polite”) style. It’s what you’d use in everyday conversation with most people—strangers, coworkers, acquaintances—unless you need to be more formal or more casual.

Why don’t we use the honorific form 계세요 instead of 있어요?

계세요 is the honorific counterpart of 있어요, used when the subject deserves respect (e.g. elders, customers). Here you’re talking about your own family in a neutral way, so 있어요 is fine. If you specifically wanted to honor them, you could say 가족분들이 집에 계세요.

Do I need 제 가족 or 우리 가족 to mean “my family”?

In Korean you often drop the possessive when it’s clear from context. 가족이 집에 있어요 naturally means “My family is at home.” If you want to be explicit, you can say 제 가족이 집에 있어요 or 우리 가족이 집에 있어요, where 우리 can colloquially stand in for “my.”

How would I form the past tense of this sentence?

Simply change 있어요 to 있었어요:
• 가족이 집에 있었어요
This means “My family was at home.”

How do I turn this into a question?

You can add a question mark and use rising intonation:
• 가족이 집에 있어요?
That means “Is your family (or my family) at home?”

Can I drop the particle 이 and say 가족 집에 있어요 for a more casual feel?

In very casual spoken Korean (e.g. among close friends), some particles get dropped, but it’s not standard. For clarity and correctness, especially in writing or polite speech, keep 이: 가족이 집에 있어요.

What’s the difference between 있다 for location and 있다 for possession?

Both uses share the same verb 있다, but the structure differs:
• Location: [place] + 에 + 있다 → 집에 있다 (“be at home”)
• Possession: [possessor] + 에게/한테 + [item] + 이/가 + 있다 → 저한테 시간이 있어요 (“I have time”)
In location you mark where something exists; in possession you mark who has something.