42　不定式的逻辑主语　Track40

（1）何谓逻辑主语？
对于三种非谓语动词而言，都有一个逻辑主语的问题，这是因为它们都是动词的变化形式，既然是动词就应该有动作的执行者，即主语。之所以称之为逻辑主语，这是为了区别于句子主语。因为句子主语和非谓语动词的逻辑主语并不总是一样的。请比较：

 
对于动名词和分词，同样存在句子主语和逻辑主语一致或不一致两种情形。具体后文再进行讨论，在此先分析不定式的逻辑主语。
（2） for sb. to do
不定式的逻辑主语常见的是由“for + 名词 / 代词”引出，这里的“名词 / 代词”即是不定式的逻辑主语，来说明不定式动作的执行者。
a.It's important for you to go there in person.
你有必要亲自去那儿一趟。
b.It is very common for him to be absent without leave.
不请假就擅自离开是他的一贯作风。
c.He was very willing for everyone else to come.
他很愿意让其他所有的人都来。
d. For any adhesive to make a really strong bond, the surfaces to be glued must be absolutely clean and free from moisture or grease.
对于任何黏合剂，要想粘得牢固的话，则被粘的表面必须绝对清洁且不能潮湿和有油性物质。
e.The father will be proud for his son to win the gold medal . (=...if his son wins the gold medal.)
f.The eye of an animal is quite easy to see. How then can the eyes be prevented from spoiling the animal's blending with its environment? One solution would be for the animal to keep its eyes closed when danger threatens.
下列句子因为不定式的逻辑主语不明确而显得不规范，因此在写作文时要避免。
g.To study English well, a lot of practices are needed.*
h.A lot of practices are needed to study English well.*
g，h两句要表达的意思是：“要想学好英文，大量练习是必要的。”但完全是受汉语思维影响而写出的句子。
以上两句均因句子主语a lot of practices不能作不定式to study的逻辑主语而显得不规范。因此，上面两句可以改为：
i.To study English well, you need a lot of practices.
j.A lot of practices are needed for you to study English well.
k. For you to study English well, a lot of practices are needed.
（3） of sb. to do
用来说明人的性格特征或行为表现的动态形容词与不定式连用时，用“of +名词 / 代词”这一结构引出不定式的逻辑主语。这样的形容词主要有：
brave　careful　careless　clever　cruel　foolish
generous　kind　modest　nice　polite　rude
selfish　silly　stupid　thoughtful
a.It's wise of you not to argue with your boss.
b.It's generous of him to lend me his car.
c.It was very careless of him to make such silly mistakes.
for和of的使用规律是：看句中的表语形容词是着重说明人（逻辑主语）还是事（不定式短语）。若是前者，则用of；若是后者，则用for。另外，用of的句子，可以用人作主语将句子改写，用for的句子则不能。试比较：
d.You are important to go there in person.*
e.It's important for you to go there in person.
f.You are wise not to argue with your boss.（逻辑关系正确）
g.It's wise of you not to argue with your boss.