相关问题好像我们以前私下谈论过，在外地，就简单把以前查阅的整理一下，供参考。

第一点，不定式作条件状语是个古老现象，最初，带着to的不定式在古英语时期主要是表示目的，表示将来性，假设性，潜在性，后来，在to的目的作用减弱后，为了达到强调目的的作用，人们甚至又在前面加了个for，用for to来加强其目的含义。到了中古英语时期，to 不定式越来越多地被用来代替虚拟语气，所以，从历史上看，表示假设条件本就是其功能之一，不是现代产物，只是可能真实非真实条件交叉混用，有时不好区分了。这种条件假设我觉得一部分也可以理解为原因（你说的Swan老先生的观点），但不是整体性特征，其根本仍然是假设条件。to的意义的模糊性让语法家们也很为难，例如早期的Poutsma就曾写道：But in many adverbial and adnominal clauses the meaning of to is vague and weak, often to the extent of being hardly discernible. Thus in Scrooge hung his head to hear his own words quoted by the spirit; I rejoice to see you; You' re in luck to come today; To hear him, you would think he had passed half his life in Australia;

关于The most likely origin of the to-infinitive is what I have called the purposive to-PP, to be distinguished from the spatial to-PP. Purposive to-PPs do not express a goal in space, but in time, i.e. a future, or at least non-actuated, event. The equivalence between to-infinitive and subjunctive clause means that the to-infinitive was reanalysed at some point as a non-finite subjunctive. This means that to has the same features to check as the subjunctive, and like the subjunctive it checks them in T. （w相关资料大家可参阅《The Rise of the To-Infinitive》）

第二，我也引一些不定式表示条件的例子：Infinitive clauses of condition

These infinitive clauses are not introduced by subordinators.

211. a. You would be a fool not to apply for that job.

b. To survive, we must have food.

c. To hear her talk, you’d think she was a doctor.

d. To see them together, you’d think they were husband and wife. (If we are to judge by what we have seen…)

e. To get to the station, we’ll have to take a taxi.

f. To get to the station, we had to take a taxi.《Non-finite Clauses in English Formal Properties and Function》

第三，关于楼主所问二者的区别，我引国内秦裕祥老师的文章观点不定式一般表示主观性意义, -ing分词则主要表示客观性意义。据此, 含强烈主观性意义的目的状语用不定式表示, 含有明显客观性意义的时间状语、方式状语、伴随状语等则用 -ing分词表示。

有些状语, 如条件状语、结果状语、让步状语和原因状语等则主观性意义和客观性意义兼而有之。一般说来, 主观性意义较强时用不定式, 客观性意义较强时用 - ing分词。现分述它们的用法区别。

1. 作条件状语时的区别

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 by 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情况。如它用于表示说话人主观设定的条件或与目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.

To make others comfortable, you have to appear comfortable yourself.

-ing分词表示的条件多为真实条件, 但它偶尔也可表示非真实条件, 表明说话人对普遍事实的假设。例如:

Having to live on my knees, I would rather die.

This same thing, happening in wartime, would amount to disaster.

由上述情况得知, 不定式与 -ing分词表示的条件意义有一定的差别, 使用时不可随意交换。试比较:

To hear /? Hearing him talk, you would think him to be a celebrity.

Turning /? To turn to the left, you will find the path leading to the site .

Judging /?To judge by the look on his face, he doesn’t think much of our local wine.

To put /? Putting it mildly, she’s just a bit inquisitive.

比较显示, -ing分词指泛指或业已发生的特定动作, 不定式则指假定要发生或即将要发生的动作。另有一点值得注意, 表条件时, -ing分词只有一般体形式, 不定式则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, 但在有些句型中, 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:

a. I should be glad to go (= if I could go).

b. I should have been glad to go (= if I could have gone) .

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 ) .

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 France.