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 1）; 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 2.
⑩ swimming makes us hale and 3.
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 4 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）
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