不定式可以作定語。不定式在句中作定語，置于被修飾的名詞或代詞之后。如：①The next train to arrive is from Washington.下班車來自華盛頓。②Do you have anything to be taken to your sister?有什么需要帶給你妹妹的么？

不定式形式

1) 一般式：一般現(xiàn)在時表示的動詞，有時與謂語動詞表示的動作同時發(fā)生，有時發(fā)生在謂語動詞的動作之后。一般為：動詞+ to do something

He seems to know this.

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

2) 完成式：表示的動作發(fā)生在謂語動詞表示的動作之前。

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

He seems to have caught a cold.

3)進(jìn)行式：表示動作正在進(jìn)行，與謂語動詞表示的動作同時發(fā)生。

He seems to be eating something.

4)完成進(jìn)行式：

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

一般在表示情緒的動詞后加to do也表將來

疑問詞

疑問詞who,what,which,when,where,whether,how后可接不定式構(gòu)成不定式短語，在句中作主語、賓語、表語等。如：

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

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

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

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

以上例句中疑問詞+不定式部分，均可轉(zhuǎn)換為相應(yīng)的從句形式。