Learn Hardcore Korean: chingudeuri gongwoneseo norayo.

-들 is the plural marker in Korean. It turns 친구 (friend) into 친구들 (friends). It’s optional—Korean often leaves nouns unmarked for number—but adding -들 makes it clear you mean more than one friend.

Why do we attach 이 after 친구들? Couldn’t we use 가 instead?

이/가 are both subject markers, but you choose based on the final sound of the noun: • Nouns ending in a consonant take 이 (친구들 → 친구들이).
• Nouns ending in a vowel take 가 (학교 → 학교가).
They both mark the noun as the subject of the verb.

What’s the difference between the markers 은/는 and 이/가?

• 은/는 is the topic marker: it introduces or contrasts the topic of conversation.
• 이/가 is the subject marker: it indicates who or what is performing the action or existing in a state.
In 친구들이 공원에서 놀아요, using 이/가 highlights who is playing (i.e. the friends) rather than making friends the general topic.

What does 공원에서 mean, and how does -에서 function here?

-에서 is the location particle used with action verbs.
• 공원 means “park.”
• 공원에서 놀아요 literally means “(they) play at/in the park.”
-에서 tells you where the action takes place.

Why is 놀다 conjugated as 놀아요 here? What does -아요 indicate?

-아요 is the polite present-tense verb ending for stems with the vowel ㅏ or ㅗ.
Verb stem: 놀- (from 놀다, “to play”)
Conjugation: 놀 + 아요 = 놀아요
This makes the sentence polite and present tense.

How would you change this sentence to past tense?

Use -았어요 for stems with ㅏ or ㅗ: • Stem: 놀-
• Past tense: 놀 + 았어요 = 놀았어요
So it becomes 친구들이 공원에서 놀았어요. (“My friends played at the park.”)

How do you turn 친구들이 공원에서 놀아요 into a question?

You can simply raise your intonation at the end in spoken Korean: • 친구들이 공원에서 놀아요?
Or use a more formal question ending -습니까?: • 친구들이 공원에서 놉니까?
Both forms ask “Are (my) friends playing at the park?”