Learn Hardcore Korean: gageeseo chaegeul sayo.

The particle 에서 marks the location where an action occurs. In 가게에서 책을 사요, it tells us that the buying takes place at the store. You can think of it as “at” or “from” when describing where an activity happens.

What’s the difference between 에서 and 에 when talking about places?

에 indicates a static location (e.g., 학교에 있어요 “I am at school”) or a destination (e.g., 집에 가요 “I’m going home”).
에서 specifically marks the place where an action takes place (e.g., 도서관에서 공부해요 “I study at the library”).
So use 에서 when you have a verb of doing something, and 에 when you’re describing existence or movement.

Why is the object particle 을 attached to 책?

In Korean, the particle 을 (or 를 after a vowel) marks the direct object of a verb. Here, 책을 means “(the) book” is what you’re buying. Without 을, the sentence would be incomplete or ambiguous about what’s being bought.

How do we get 사요 from the verb “to buy”?

The dictionary form of “to buy” is 사다. To conjugate into the present polite form, you:

Drop 다, leaving the verb stem 사-.
Add -아요 (because the stem vowel ㅏ pairs with -아요).
Result: 사
- 아요 → 사요.

What level of formality is 사요?

사요 is in the polite informal (해요체) style. It’s suitable for most everyday situations with people you’re not extremely close to, or when you want to be respectful but not overly formal. It’s more polite than the casual 사 and less formal than 삽니다.

Can the subject (e.g., 저는 or 나는) be omitted here?

Yes. Korean often drops subjects and objects when they’re clear from context. In 가게에서 책을 사요, the subject “I” is implied. If you want to specify, you could say 저는 가게에서 책을 사요 (“As for me, I buy a book at the store”).

Is the word order flexible? Could you say 책을 가게에서 사요?

Yes, you can say 책을 가게에서 사요 without changing the meaning. Korean is relatively flexible because particles mark each word’s role. However, the most neutral order is [Location]에서 + [Object]을 + [Verb].

How would you turn this sentence into the past tense?

To make it past tense in polite informal style, change -아요 to -았어요 (because the verb stem vowel is ㅏ):
사다 → 사 + 았어요 → 샀어요
Full sentence: 가게에서 책을 샀어요 (“I bought a book at the store.”)

How can I make this a question?

In Korean, you turn a statement into a question simply by adjusting intonation or adding -요? at the end. Here are two options:

Intonation change: 가게에서 책을 사요? (rising tone)
With a question marker: 가게에서 책을 사나요? (more formal)
Both mean “Do you buy a book at the store?” or “Are you buying a book at the store?” depending on context.