介词和介宾短语
Prepositions and their phrases

第五级你说过“我跟朋友一起去”“从我家到学校要半个小时”“他对我笑了笑”。“跟、从、对”都不是动词，可是后边都带着一个名词，而且这一组词全站在动词前边。你也从来没说过“我看书在图书馆”——英语正是这个次序，汉语听着就不对。这一课说清楚为什么。

Level 5 taught you 我跟朋友一起去, 从我家到学校要半个小时, 他对我笑了笑. The words 跟, 从, 对 are not verbs there, yet each carries a noun behind it, and the pair always stands in front of the verb. You have never said 我看书在图书馆 either — which is exactly the English order and sounds wrong in Chinese. This lesson says why.

介词一个字用不了，后边必须有东西。宾语可以是名词、代词，也可以是方位短语：在桌子上、从他那儿。注意“我在吃饭”的“在”不是介词，那是副词，说的是动作正在进行；“我在家吃饭”的“在家”才是介宾短语。

A preposition is never usable on its own — something must follow it. The object may be a noun, a pronoun or a place phrase: 在桌子上, 从他那儿. And watch out: the 在 of 我在吃饭 is not a preposition but an adverb marking the action as under way. Only 在家 in 我在家吃饭 is a 介宾短语.

状语是动词前边说明情况的那一部分：时候、地点、方式、对象都在这儿。汉语的次序是先交代情况，再说动作，所以介宾短语一律前置。英语说 I read books at the library，汉语只能说“我在图书馆看书”。少数几个介词可以留在动词后边——住在北京、放在桌子上、来自上海——那是因为它们已经跟动词长在一起了。

The 状语 is the part in front of the verb that sets the scene: time, place, manner, the person addressed. Chinese states the circumstances first and the action second, so a preposition phrase is always fronted. English says 'I read books at the library'; Chinese can only say 我在图书馆看书. A handful of prepositions do stay behind the verb — 住在北京, 放在桌子上, 来自上海 — because they have fused with the verb into one word.

一个词两个身份，靠位置分：后边还有一个动词，它就是介词；后边没有动词，它自己就是谓语的中心。“我在家”只有一个“在”，那是动词；“我在家吃饭”后边来了“吃”，“在”就退了一步。正因为来源是动词，介词有时候读起来也像动词——这是汉语和英语很不一样的地方。

One word, two identities, and position decides which: if another verb follows, it is a preposition; if none does, it is itself the head of the predicate. 我在家 has only 在, so 在 is the verb. Add 吃 and 在 steps back. Because of that verbal origin, English grammars of Chinese often call these words coverbs rather than prepositions.

动词能重叠（看看、等一等），能带“了、过、着”（去了、去过），还能单独回答问题（你去吗？——去）。介词三样都做不到：说不出“从从”，说不出“从了北京来”，人家问“你从哪儿来”，你也不能只回答一个“从”。碰到拿不准的词，用这三条量一量就清楚了。

A verb can reduplicate (看看, 等一等), take an aspect marker (去了, 去过) and answer a question by itself (你去吗? — 去). A preposition can do none of the three: there is no 从从, no 从了北京来, and asked 你从哪儿来 you cannot reply with a bare 从. When a word leaves you unsure, run it past these three tests.