可放句首當主詞。

To safeguard the factory from being further burglarized, it is decided that new detection equipment is to  be purchased.   

例句：

規律運動是很重要的。

To exercise regularly is important.

可補充說明虛主詞 “it”。

It is important to exercise regularly.

[虛主詞]       [真正的主詞] 可放動作後當受詞。  

例句：

我不想聽你的藉口。 I don’t want to listen to your excuses.

不定詞

不定詞為「to + 動詞原形」所組成，

而不定詞的否定則為「not to + 動詞原形」。

例句：

媽媽叫我不要熬夜。她叫我早睡。

Mom tells me not to stay up late. She tells me to go to bed early.

「不定詞」的用途如下：

1.可放句首當主詞。    

例句：

規律運動是很重要的。

To exercise regularly is important.

可補充說明虛主詞 “it”。

It is important to exercise regularly.

[虛主詞]       [真正的主詞] 可放動作後當受詞。  

例句：

我不想聽你的藉口。 I don’t want to listen to your excuses.

2.可放名詞後當形容詞。

例句：我無話可說。 I have nothing to say.

3.可表「為了…」  

例句：

為了看清楚，我戴上我的眼鏡。

To see well, I put on my glasses.

「太…以至於不能…」：too 形/副 to 動詞原形

例句：他太生氣以至於說不出話來。

He's too angry to say a word.

「夠 … 足以 …」：形/副 enough to 動詞原形      

例句：他夠勇敢，敢說實話。

He's brave enough to tell the truth.

例句:

To make sure that the deal could be closed successfully, the manager ruled that everyone in the advertising section work till ten every night last week.