eoje ilgdeon chaege chaekgalpireul kkoja dueosseoyo.

I left a bookmark in the book I was reading yesterday.

Breakdown of eoje ilgdeon chaege chaekgalpireul kkoja dueosseoyo.

• 읽다: to read
• 책: book
• ~를: object particle
• 어제: yesterday

Questions & Answers about eoje ilgdeon chaege chaekgalpireul kkoja dueosseoyo.

Why is it 읽던 and not 읽은 in 어제 읽던 책?

This is one of the biggest grammar points in the sentence.

• 읽은 책 = the book that I read / have read
  • This sounds more like the reading is viewed as a completed event.
• 읽던 책 = the book I was reading / had been reading
  • This often suggests:
    • the action was ongoing in the past,
    • it may have been unfinished,
    • or the speaker is recalling something from experience.

So 어제 읽던 책 most naturally means the book I was reading yesterday, not simply the book I read yesterday.

In this sentence, that nuance fits well because if you put a bookmark in it, you probably had not finished the book yet.

What nuance does -던 add exactly?