to do可以放在句首吗（todo结构位于句首可表条件）

尽管中高考英语还没有考查到这点，但我们也要知道句首的不定式——无疑是可以表达条件（从句）的含义的。

《新编高级英语语法》（章振邦主编）第534页

不定式分句还能表示条件，通常置于句首。例如：

To listen to him, you should think that no problem whatever existed（什么问题也没有）.

To hear him talk, you would think he owned the whole world.

《英语语法大全》（张道真编著下）第590页1124

(3)作状语的不定式表示条件。

在不定式这样用时，谓语中常包含will, shall, should, would, must, can或could这样的助动词。

To say such a clever thing, he can’t be a fool.

To see her, you wouldn’t believe she is already forty.

To be really useful, a book must be read several times.

To study music, one must start at six.

外研社《英汉多功能词典》第2253页to第9词条：

to（表条件）一旦……（就会认为）：

To take with him, you would think he is a warm-hearted man, but in fact he isn’t.

一旦你和他聊一下，就会认为他是一个热心的人，其实不然。

《大学英语语法——讲座与测试》第五版第612页2：

有时候，作主语的不定式相当于一个条件从句。例如：

To love others is to be loved. = If you love others, you will be loved by others.

爱人即爱己。

To build an expressway across the country requires a lot of money.

= If you build an expressway across the country, it will requires a lot of money.

建一条贯通全国的高速公路需要很多钱。

To see her is to love her. 见了她就会爱上她。

= If one loves her, one will love her.

《王国栋国际英语深层语法》第277页4：

条件状语：通常置于句首，用逗号隔开。如：

To hear him speak, you would think he owned the whole world.

= If you should hear him speak, you would think he owned the whole world.

所过你要是听信他讲的话，你会认为他拥有全世界。

《英语语法大全》（伦道夫·夸克等著）第1509页

[g]不定式分句有时同时表示条件和其他相应的关系，如目的和原因：

You’d be a fool not to take the scholarship. [“if you didn’t …”]

To be considered for admission, you must make a formal application.

[“If you are to be considered…”, “In order to be considered…”]

事实上，如果不定式结构置于句首表达“条件（从句）”的含义放入高考英语真题中去考察的话，那么可以看到有些命题是不严谨的。

按照惯例，本届高考学生还是以to do sth位于句首，可以充当目的状语，或是作主语这两种形式为主更好。

2017年4月21日