一、动词不定式作条件状语的历史传承
动词不定式作条件状语至少可以追溯到成书于1931年George O. Curme 著的Syntax，并且被中外的语法学家所认可，传承至今。以下是动词不定式作条件状语的历史传承：
1. George O. Curme 著Syntax(1931年版) (汪璜译《英语句法》商务印书馆 1989年8月第1版)(上册)P581:
“I was thinking of asking ￡30 for the month.”(for the use of the boat)―“The boat is not worth it to buy.”(=if one should buy it for that price)
《英语句法》(下册)P201:
I should be glad to go (= if I could go).
I should have been glad to go (=if I could have gone).
He would have been foolish to do it (=if he had done it).
2. R. W. ZANDVOORT 著 A Handbook Of English Grammar (First published 1957)P10： In so-called “free-adjuncts”, the idea of purpose may be weakened, and even shade off into that of circumstance or condition.
To hear him talk, you’d think he knew all about the subject.
3. 李绍基编著的《英语非谓语动词》（译林出版社1981年12月第1版）P68：动词不定式短语有时也可用来表示一定条件，其产生的结果往往带有虚拟或主观推断的性质，因此句中的谓语动词前常用should, would, could, must等词。例如：
To hear him talk, you would think he owned the whole world.(=If you should hear him talk, …)
To look at him, you could hardly help laughing.
To listen to him, you should think that no problem whatever existed.
To judge by her reaction, she must deeply felt angry at your remarks.
You would be a fool to refuse this offer.
I should be sorry to see such a day.
4. 冯明仪编《英语非限定动词》(广东教育出版社 1986年6月第1版)P46: 5.表示条件动词不定式表示条件，常见于虚拟语气中。例如：
I should be glad for Mary to go. (= I should be glad if Mary went.)
You should have done better to have made up with them.(= You should have done better if you had made up with them)
5. 刘乐亭编著的《英语五难题》(北京出版社 1989年2月第1版)P247: 3）作条件状语
To hear him speak English, one would take him for an English man.
6. 卢盛莽编著的《英语非谓语动词疑难详解》(辽宁大学出版社1989年12月第1版)P113:4）作条件状语。不定式常用于句首，主句谓语动词多用于虚拟语气。
To listen to him, you should think that he has gone there. (笔者注：gone应为been)
To hear him talk, you should think he owned the whole world.
7. 李永生主编《实用英语语法》(光明日报出版社 1990年10 月第1版)P169：
To hear him talk, you would think he owned the whole world.（条件）
8. L. G. Alexander著 的Longman English Grammar《朗曼英语语法》(雷航等译，外语教学与研究出版社1991年1月第1版)P533：
To hear him talk, you’d think he was Prime Minister.(=if you could hear him talk)
9. 刘毅编著的《英语语法宝典》(北京师范大学出版社 1993年12月第1版)P231:
表条件
You would make a great mistake to take his bribe.
(=You would make a great mistake if you took his bribe.)
I should be happy to be of any service to you.
(=If I am of any service to you, I should be happy.)
To hear him talk, you would take for a scholar.
(=If you heard him talk, you would take for a scholar. )
10. 何桂金编著《英语动词新编》(重庆大学出版社 1996年7 月第1版)P247: 7)修饰整个句子表示条件。例如：
I’ll thank you not to follow me. (= if you don’t follow me)
To look at him (If you looked at him), you could hardly help laughing.
11. 张道真编著的《英语语法大全》上册（外语教学与研究出版社1998年8月第1版）P711:
I should have been very pleased to have been present.
The servant would not have quitted to have been better treated.
12. 秦裕祥著的《英语语法专题研究》（湖南师范大学出版社 1999年5月第1版）P180：不定式表示想象性条件，主要用于表示说话人的假设。例如：
To hear him talk, you would think he owned the whole world.
A man would be blind not to see that.
To judge be her reaction, she must have deeply resented your remarks.
不定式表示的条件多为非真实条件，但有时也可见到不定式表示真实条件的的情况。如它用于表示说话人主观设定的条件或与目的的意义相混杂的条件时即是如此。
You do an honest man wrong to call him a liar or a thief.
You have to be strong to lift a table like that.(笔者注：此句可参考18. )
To make other comfortable, you have to appear comfortable yourself.
13. 徐广联主编的《大学英语语法讲座与测试》(第二版)(华东理工大学出版社 2000年)P569: 6) 表示条件 动词不定式有时也可以表示条件。一般置于句首，否定不定式多置于句尾。例如：
To look at her, you would think her a young woman, but she is in fact 47 years old. (= If you were to look at her)
One would be careless not to see the mistakes. (=if one should not see…)
You couldn’t do that to save your life.
I should have been sorry to have missed the chance.
14. 张满胜编著《英语语法 新思维高级教程：驾驭语法》(世界知识出版社 2002年4 月第1版)P200: 3. 用作条件状语
You would be stupid not to ask for a raise.= You would be stupid if you don ‘t ask for a raise.
I would be very happy to be invited to the party.=… if I had been invited …. But I wasn’t invited.
15. 薄冰编著《高级英语语法》最新修订)(世界知识出版社 2002年10 月第8次印刷) P295: 5)不定式偶尔亦可表让步或条件。如：
To look at him you could hardly help laughing.
A man would be blind not to see that.
16. 贺立民编著《贺氏英语语法全书》(中山大学出版社2003年2月第1版)P764: 15.表示“条件”――相当于一个 if-clause。如：
To hear you sing, people might take you for a girl.= If people heard you sing, they might take you for a girl.
17. 王国栋编著的《大学英语深层语法》(清华大学出版社 2005年1 月第1 版)P334：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.
18. 张克礼编著《新英语语法》（第二版）（高等教育出版社 2005年1月第2版）P221: (5)表示条件，可取代条件状语从句：
I should be delighted to join you/if I could join you.
He would have been foolish to do it/if he had done it.
不定式分句有时把条件和其它语义结合在一起，如目的、理由等：
You must be strong to lift that weight.
= You must be strong if you are able to lift that weight.
= You must be strong in order to lift that weight.
= You must be strong because you are able to lift that weight.
19. 赵振才编著《英语常见问题解答大词典》(增订版)(世界图书西安出版公司2005年3月第1版)P684: 除了非真实条件状语从句之外，还有许多语言手段来表达非真实的情况。动词不定式便是此种手段之一。动词不定式用作条件状语时，它不是通过词汇手段（如，if, as long as, provided等），而是通过语法手段来表示条件关系的。
You would do well to write more distinctly.(事实是：你写得不清楚，动词不定式to write more distinctly提出与事实相反的条件)
In fact, the nation’s first settlers would have been very surprised to see how Americans celebrate Christmas today. (VOA)事实上，要是美国最早的定居者看到今天美国人庆祝圣诞节的盛况，会感到十分惊讶。
P685：【问】I would have given much to have been able to call off the whole thing.(复旦大学等校编《大学英语》精读4级一单元)
我们班很多同学将上面的句子理解为“为了能够取消这件事，我宁愿做出很大牺牲”。不知这种理解是否正确？
【答】当看到主句中的would have given这一虚拟形式时，就应想到to have been able一定跟非真实条件有关。完成体不定式（to have been able）更能显性地表示与过去事实相反的条件。上面句子的意思是：要是那时我能够取消整个这件事的话，那我是多大的牺牲都愿做出来的。
20. [日] 绵贯阳等著《现代英语语法例解手册》(修订版))(申勇译 科学出版社2006年2月第1版)P463:(5)表示条件。也用于虚拟语气的句子结构。
To hear him talk, you would take him for a foreigner.
P539: You’d be crazy to expect that kind of thing to happen.(=If you were to expect that kind of thing to happen,…)
To hear him talk, you would think he was God Almighty. (=If you heard him talk, …)
21. 杨元兴主编《英语句型大全》(上海外语教育出版社2007年3月第1版)P1037：不定式短语也可表示真实条件，但不常见。
I’ll thank you not to follow me (=if you do not follow me).
To survive (=If we are to survive), we must have food.
P1044:不定式短语表示非真实条件。
It would be easier to do it this way (=if we were to do it this way).
To look at him (=If you were to look at him), you could hardly help laughing.
To hear him speak English (=If one were to hear him speak English), one would take him for an Englishman.
22. 章振邦主编的《新编高级英语语法》（上海外语教育出版社2012年12月第1版）P514：
To look at him (=If you were to look at him), you would think him a young man.
One would be a brute not to feel for the sufferings of the black people in
23. 刘永科主编的《高中英语语法全解》（陕西人民出版社2013年3月第1版）P191：
You would be a fool to refuse his offer.
=If you should refuse his offer, you would be a fool.
24. 徐广联主编的《大学英语语法讲座与测试》(第5版)(华东理工大学出版社 2014年1月第5版)P623: 6) 表示条件 动词不定式可以表示条件，一般置于句首，否定不定式多置于句尾。不定式表示条件时，句中谓语常含有will, shall, should, would, can, must等。例如：
To look at her, you would think her a young woman, but she is in fact 47 years old.(= If you were to look at her)
One would be careless not to see the mistake.(= if one should not see)
How can you catch the train to star so late?
You couldn’t do that to save your life?
You do an honest man wrong to call him a liar.
You will do better to get her support.(=if you get her support)
To be successful, one must do one’s best.
I should be very happy to be of service to you.
One will get into trouble to do such a thing.
To be a masterpiece, the book needs revising again and again.
You will regret one day for your son to marry her.
I should have been sorry to have missed the chance.
She would have been astonished to have received a letter from a stranger.
二、对“动词不定式作条件状语”的不同看法
当然，有的语法学家“动词不定式作条件状语”的不同看法，例如Michael Swan在其编著的《牛津英语用法指南》(第二版 翻译本)(外语教学与研究出版社2000年9月第1版) P365和《牛津英语用法指南》(第三版 翻译本)(外语教学与研究出版社2010年4月第1版) P427认为：see 和hear的动词不定式可用来解释产生假象的原因。这类动词不定式结构之后通常跟you’d think或类似的表达方式。
To see them, you’d think they were married. But they only met yesterday.
To see him walk down the street, you’d never know he was blind.
To hear her talk, you’d think she was made of money.
笔者认为以上三句与其看作“动词不定式做原因状语”，倒不如看作“动词不定式做条件状语”更易于理解。例如，把“To see him walk down the street, you’d never know he was blind.”改为原因状语从句，应为You’d never know he was blind because you see him walk down the street.很难理解。但是，改为“动词不定式做条件状语”，应为If you see him walk down the street, you’d never know he was blind. if从句表示非真实的条件，很容易理解。
三、“动词不定式作条件状语”能否划为“动词不定式做原因状语”
事实上，动词不定式作状语时，很难区分究竟是条件还是原因，例如，在上面提到的张克礼编著的《新英语语法》（第二版）（高等教育出版社 2005年1月第2版）P221就认为： 不定式分句有时把条件和其它语义结合在一起，如目的、理由等：
You must be strong to lift that weight.
= You must be strong if you are able to lift that weight.
= You must be strong in order to lift that weight.
= You must be strong because you are able to lift that weight.
再如，上面提到的秦裕祥著的《英语语法专题研究》（湖南师范大学出版社 1999年5月第1版）P180认为：如用于表示说话人主观设定的条件或与目的的意义相混杂的条件时即是如此。
You do an honest man wrong to call him a liar or a thief.
You have to be strong to lift a table like that.(笔者注：此句与上面的句子及其相似！ )
然而，不能因为有些“动词不定式作条件状语”（笔者注：大多数语法学家的看法）的句子能够改为“动词不定式作原因状语”，就以偏概全地错认为所有的“动词不定式作条件状语”的句子都可以划为“动词不定式作原因状语”。
下面拿以上提到的赵振才编著的《英语常见问题解答大词典》(增订版)(世界图书西安出版公司2005年3月第1版)P684:的一个句子为例：In fact, the nation’s first settlers would have been very surprised to see how Americans celebrate Christmas today. (VOA)事实上，要是美国最早的定居者看到今天美国人庆祝圣诞节的盛况，会感到十分惊讶。
此句可以改为条件状语从句: In fact, the nation’s first settlers would have been very surprised if they could see how Americans celebrate Christmas today. 事实上，要是美国最早的定居者看到今天美国人庆祝圣诞节的盛况，会感到十分惊讶。
但是绝对不能改为原因状语从句：In fact, the nation’s first settlers would have been very surprised because they could see how Americans celebrate Christmas today. 事实上，因为美国最早的定居者看到今天美国人庆祝圣诞节的盛况，会感到十分惊讶。（笔者注：此句太不可思议！）
仅此一例就足以证明把“条件状语从句”划到“原因状语从句”的观点是错误的！
况且，动词不定式作条件状语和作原因状语是有差别的：
1. 潘焕怀编著的《现代英语句法》（北京师范大学出版社 1984年9月第1版）P206不定式短语可以用于动词、形容词或-ed分词后表示原因。表示原因时，不定式短语表示的动作先于谓语动词表示的动作。例如：
I’m sorry to hear you are not well.
2. 徐广联主编的《大学英语语法讲座与测试》(第5版)(华东理工大学出版社 2014年1月第5版)P622：不定式作原因状语时，一般放在句尾，不定式常跟在一些 形容词或过去分词后说明产生这种情绪的原因，常用的这类词有：happy, lucky, fortunate, pained, ashamed, surprised, grieved, frightened, shocked, sorry, glad, delighted, eager, disappointed, right, anxious, ready, clever, unwise, quick, foolish, rude, considerate, cruel, wrong, annoyed, bored, astonished, interested, overjoyed, puzzled, relieved, worried等。例如：
He is rude to behave like that.
3. 秦裕祥著的《英语语法专题研究》（湖南师范大学出版社 1999年5月第1版）P185：不定式表示 两种原因，一是激发性原因，这时它出现于含情感意义的词语之后，表明激发人类喜怒哀乐等情感的原因；二是说明性原因，这时它出现于描述人类品格或性质特征的词语之后，表明说话人作出评论的理由。例如：
The audience cheered to see our team win. (the fact that they saw our team win caused them to cheer.)
He looked happy to hear the news. (The fact that he heard the news made him look happy.)
He was fortunate to escape being hurt. (The reason why I think he was fortunate is that he escaped being hurt.)
不定式表示原因时，终止性动词倾向于用一般体表示先时性；延续性动词或终止性动词在特别强调先时性时用完成体表示先时性。
4. 秦裕祥著的《英语语法专题研究》（湖南师范大学出版社 1999年5月第1版）P180：
不定式表示想象性条件，主要用于表示说话人的假设。 (例句见12.)
不定式表示的条件多为非真实条件，但有时也可见到不定式表示真实条件的情况。如它用于表示说话人主观设定的条件或与目的的意义相混杂的条件时即是如此。(例句见12.)
表条件时，不定式有一般体和完成体形式，一般体主要表示对说话时刻后的情况的假设，但在有的句型中，也可表示对说话时刻前的情况的假设，完成体则仅表示对说话时刻前的情况的假设。试比较：
(1) A. I should be glad to go(=if I could go).
B. I should have been glad to go(if I could have gone).
(2) A. He would be foolish to do it (=if he should do it)
B. He would have been foolish to do it (=if he had done it)
(3) A. To have come (=if you had come) to good terms with them, you would have done better.
B. What would I give not to have heard (=if I had not heard) the calamities fallen on the heads of the King and Queen of
C. What would I not have given to be able (=if I had been able) to say the rules without a mistake!