话题句【huàtíjù】

A sentence can open with its topic – the thing being talked about – and then give the comment. The topic is often what English would put after the verb as the object, moved to the front because both speakers already have it in mind.

The comment is a complete clause in normal order; only the topic has moved. 我看过这本书 is also correct. Fronting the object makes "this book" the starting point – someone has just mentioned it, or you're setting it against something else.

The topic must be known

Only something definite can be a topic: a thing already mentioned, marked with 这 or 那, or general enough that everyone knows it. A new, indefinite object stays after the verb.

• × 一本书我买了 → 我买了一本书
• × 一个朋友我昨天见了 → 我昨天见了一个朋友

With 都 and 也

A fronted topic often comes with 都 or 也, which point back to it. In 这些菜我都喜欢, 都 covers the dishes, not me.

A topic, then one part of it

The topic can be a person or thing, and the comment describes one part of it. 他个子很高 is "he is tall" – literally "him, height is high". There is no 的 between them and no 是.

• × 大象是鼻子很长 → 大象鼻子很长