英语动词有限定（finite）和非限定（non-finite）两类。

句子中的谓语动词（predicative verb）是限定的；限定动词受人称（person）和数目（number）的限制。此外，还有时态（tense ）、语态（voice）和情态（mood）等。例如：
① Good leaders serve the people whole-heartedly.
② Jason is giving a public lecture.
③ Who did it?
④ I would appreciate it if you could do me a favour.

在句子中可以施展其他功能的动词是非限定动词；这些动词具有一般动词的许多特性，但没有“人称”和“数目”的限制。

非限定动词分三种：不定式动词（the infinitive）; 分词（ the participle）; 动名词（the gerund）; 分词又分现在分词（ the present participle）和过去分词（the past participle）。

例如：
⑤ Tom found the prescribed text hard to read.
⑥ Helen has a smiling face.
⑦ Your written English is good.
⑧ Smoking is harmful to health.

⑤里的是不定式动词；⑥里的是现在分词；⑦里的是过去分词；
⑧里的是动名词。

非限定动词及其短语，语法功能庞大，涉及下列五方面：

㈠ 当主语

不定式动词和动名词都可当句子的主语，取代名词和代名词。例如：
⑨ To swim in a warm day is joyful.
⑩ Swimming makes us hale and hearty.

㈡ 当补足语

可当主语的句子成分也可当补足语。例如：
● A good government"s desire is serving the people.
● What is difficult is to hoodwink the public indefinitely.

同样的，现在分词与过去分词也可充当接系动词（the linking verb）的补足语。例如：
● The witness"s evidence is quite convincing.
● At long last, John was fully convinced.

㈢ 当宾语

不定式动词和动名词都可充当及物动词的宾语。例如：
● The baby wanted to drink milk.
● Janet suddenly stopped talking.

它们也可以成为介词的宾语，但除了“except, but, about, than”之外，介词的宾语多数是动名词。

例如：
? I am tired of repeating the same point.
? Most of us desired nothing except to succeed.
? Betty did nothing useful but talk（不带”to”）。
? That weak old man is about to die.

㈣ 当名词修饰语
? Don"t disturb the sleeping dog.（现在分词）
? Can you remove the damaged machine?（过去分词）
? That is the only thing to do.（不定式动词）
? The sailors came in a fishing boat.（动名词）

㈤ 当动词修饰语
? Walking along the road, he came across a friend.（现在分词短语）
? Extremely frightened, the picnickers fled.（过去分词短语）
? The athlete stopped to take a rest?（不定式动词短语）
? Peter came running.（动名词）