介词是描述单词之间关系的词。介词能够描述某物或某人的位置。

Example
The cup is on the table.

在上例中，介词“on”描述了杯子和桌子之间的关系。介词也能描述事件发生的时间和方式。

Example
I arrived before him.
Example
I arrived by bus.

在上例中，介词“before”描述的是“I”何时到达的时间与“him”有关，而介词“by”表示的是乘坐“bus”是到达的方式。介词的主要作用是指示地点、时间和方式。另外，介词也可用于指示所有权和目的。

Example
The purpose of this study was to develop a highly heat resistant composite with a carbon fiber base.
Example
A book is for reading.
介词的种类 介词的作用 介词示例

简单介词

用于描述位置、地点或时间

at, for, in, by, off, on, over, under

双介词

两个简单介词连用，通常用于指示方向

into, onto, upon, up to, inside, outside of, out of, from within

复合（复杂）介词

两个或两个以上的词连用，通常由一个简单介词和另一个词连用，用于表示位置

in addition to, in front of, at the back of, along with, alongside of, in comparison to, in contrast to

分词介词

分词当作介词使用

considering, including, excluding, during, regarding, provided

短语介词（介词短语）

包括介词、宾语和宾语的修饰语

for example, for instance, on time, under the influence of

目录

简单介词描述两个词（通常是名词）在位置或时间上的关系。常用的简单介词包括：at, for, in, by, off, on, over, under。

Example
The sample was placed under a microscope.
Example
We have added additional information in the revision.
Example
The board meeting starts at 9:00 am.
Example
The sample was placed under a UV light for 30 minutes.

双介词通常表示方向，由两个简单介词组成。常见的双介词包括：into, onto, upon, up to, inside, outside of, out of, from within。

Example
We ran into the apartment.
Example
Progressively higher weights were placed upon the composite.
Example
The man walked up to the officer.
Example
Strange groans came from within the box.

复合介词表示位置，至少由两个词组成。常见的复合介词包括：in addition to, in front of, at the back of, along with, alongside of, in comparison to, in contrast to。

Example
In addition to the tests to evaluate heat resistance, we also submerged the samples in water to test their varying degrees of hydrophobia.
Example
I left the package in front of the door.
Example
He picked up a soda along with the pizza.
Example
Sample 1 demonstrated high heat resistance in comparison to sample 2.

分词介词是作为介词使用的分词。它们以“-ed”或“-ing”结尾。常用的分词介词包括：considering, including, excluding, during, regarding, provided。

Example
Considering its high protein content, the sample’s resistance to heat was surprising.
Example
All of the samples, including the gold composite, were moved to a vacuum chamber.
Example
The professor talked about chirality during her lecture.
Example
The class will begin in five minutes, provided that all students are present.

短语介词（又称介词短语）由介词、介词的宾语和修饰宾语的词组成。短语介词通常以这些词开头：for example, for instance, on time, under the influence of。

Example
They arrived at the restaurant on time.
Example
You should not drive under the influence of alcohol.
Example
For example, composite A did not degenerate when heat was applied.
Example
She appreciates the flowers from her children.

人们通常认为句子不能以介词结尾。这种假设其实不对。有时，在句末不使用介词会造成句子不够自然流畅。

不自然
Is this the movie about which you told me?
自然
Is this the movie you told me about?

另外，把介词移到句子中靠前的位置能够使句子显得更加正式。

非正式
What journal was your last paper published in?
正式
In which journal was your last paper published?

在上例中，这两个句子都正确，但后一句比前一句更加正式。因此，在学术写作中，介词很少用在句子末尾。

非正式
This is a topic we previously wrote about.
正式
This is a topic that we discussed in a previous paper.

当把介词移到句子中靠前的位置时，需要注意去掉在句子末尾的介词。

错误
In which journal was your last paper published in?
正确
What journal was your last paper published in?
In which journal was your last paper published?

像形容词一样，介词也经常被滥用，即使母语是英语的作者也如此。滥用介词包括两种情况。第一种情况是在句子中错误使用介词。

错误
Where is the other student at?
正确
Where is the other student?

在上例中，介词“at”在语法上是多余和错误的。第二种情况是句子结构的写法不好，使用了太多介词。

Example
An understanding of gold composites is necessary for any company in the semiconductor industry at this time.

这种句子最好在结构上重写，使得无需使用那么多介词，示例如下。

Example
Understanding gold composites is necessary for companies in the semiconductor industry.