Learn Hardcore Korean: eoje chinguege pyeonjireul badasseoyo. - I received a letter from a friend yesterday.

어제 is a time adverb meaning “yesterday.” In Korean, time adverbs usually stand alone without particles. You can place them at the beginning or before the verb to set the time frame.

Why is the subject (e.g., 저 or 저는) omitted in this sentence?

Korean often drops the subject when it’s clear from context or previous conversation. Here, it’s understood that the speaker is the one who received the letter, so 저는 is optional and commonly omitted.

What role does the particle 에게 play in 친구에게?

에게 marks the indirect object or the source in a “receive” context. With 받다 (to receive), 친구에게 means “from a friend.” It indicates who gave you the letter.

Can I use 한테 or 에게서 instead of 에게? What’s the difference?

Yes. 한테 is the informal equivalent of 에게 (so 친구한테 = “to/from a friend”). 에게서 explicitly means “from,” so 친구에게서 편지를 받았어요 emphasizes “I received a letter from my friend.” All three are grammatically correct, but 에게서 makes the “from” meaning clearer.

Why is 편지 followed by 를?

를 is the object marker. Since 편지 (letter) is what you received, it’s the direct object of 받았어요, so you attach 를.

What does 받았어요 tell us about tense and politeness?

받았어요 is the past tense, polite (informal polite) form of 받다. The -았어요 ending signals past tense plus a polite but familiar speech level.

How would you change the sentence to make it more formal or more casual?

More formal:
어제 친구에게 편지를 받았습니다.
More casual (plain speech):
어제 친구에게 편지를 받았어.

If I want to specify “that letter,” can I say 그 편지를?

Yes. You can add a demonstrative:
어제 친구에게 그 편지를 받았어요.
This means “I received that letter from my friend yesterday.”

How can I ask “What did you receive?” referring to this sentence?

You can say:
“어제 친구에게 뭘 받았어요?”
Here, 뭘 is the contraction of 무엇을, meaning “what (object).”