这本书是我昨天买的。
zhè běn shū shì wǒ zuó tiān mǎi de.

why de?

You can just treat it as the past tense.

Break the sentence in to chunks.

zhe ben shu / shi / wo zuo tian mai de

Then, it makes more sense. The last part is basically saying what the book is, and rather than a simple assignment of an adjective it's using an embedded phrase. Most languages have this feature, it's a step up from the most basic grammar but hardly complex once you're used to it.

I am guessing you are not familiar with the (subject) (verb) (de) (object) structure in normal use, so encountering it here is confusing you. Some examples: 我买的书,小孩儿玩儿的游戏,大家爱的美女,我们西方人吃的菜. To familiarise yourself try converting each of these in to a similar sentence, eg. 这个游戏是小孩儿昨天玩儿的.

It is not the past tense: it is a genitive particle, indicating possession: the syntax is simply different to English. "This book is my having bought yesterday one," if you keep the syntax.

You see, in Chinese, when you want to use a clause as an adjective, you place 的 after the clause to indicate that the clause is a descriptor.

@voltaire "大家爱的美女"..spot on!

@大家爱的美女@ ^^ ok, it is a very very funny chinese sentence.

@小孩儿的游戏@ in the south of China, we usually do not use 儿, 小孩子 or 小孩 is better .

Thank u all!

Hello,This "de" is not a particle as usuall,it is used for a grammar "shi...de",In chinese,if we want to emphasize something we will use this.
zhè běn shū shì wǒ zuó tiān mǎi de.This sentence want to emphasize "wo zuo tian mai".For example,"the ben shu shi wo de" want to emphasize this book is mine not others'.Hope can help you!

-Dali college of Eastern language
Teacher Quan

I an Chinese native speaker,from my opinion,买的 is a pronoun。By the way,I college student and I am looking for English-speaking partner. Would you like to be my language partner？if you wanna be my partner, please contact me with the number–18788413484.Looking forward to your reply.