不定式可以作定语。不定式在句中作定语，置于被修饰的名词或代词之后。如：①The next train to arrive is from Washington.下班车来自华盛顿。②Do you have anything to be taken to your sister?有什么需要带给你妹妹的么？

不定式形式

1) 一般式：一般现在时表示的动词，有时与谓语动词表示的动作同时发生，有时发生在谓语动词的动作之后。一般为：动词+ to do something

He seems to know this.

I hope to see you again. = I hope that I'll see you again.我希望再见到你。

2) 完成式：表示的动作发生在谓语动词表示的动作之前。

I'm sorry to have given you so much trouble.

He seems to have caught a cold.

3)进行式：表示动作正在进行，与谓语动词表示的动作同时发生。

He seems to be eating something.

4)完成进行式：

She is known to have been wreaking on the problem for many years.

一般在表示情绪的动词后加to do也表将来

疑问词

疑问词who,what,which,when,where,whether,how后可接不定式构成不定式短语，在句中作主语、宾语、表语等。如：

①When to leave for London has not been decided yet. （不定式在句子中做主语）

②Mr. Smith didn't know whether to leave or stay there. （不定式在句子中做宾语）

③I asked Professor Xu how to learn English well. （不定式在句子中做直接宾语）

④The question was where to get the medicine needed. （不定式在句子中表语）

以上例句中疑问词+不定式部分，均可转换为相应的从句形式。