42　不定式的邏輯主語　Track40

（1）何謂邏輯主語？
對于三種非謂語動詞而言，都有一個邏輯主語的問題，這是因為它們都是動詞的變化形式，既然是動詞就應(yīng)該有動作的執(zhí)行者，即主語。之所以稱之為邏輯主語，這是為了區(qū)別于句子主語。因為句子主語和非謂語動詞的邏輯主語并不總是一樣的。請比較：

 
對于動名詞和分詞，同樣存在句子主語和邏輯主語一致或不一致兩種情形。具體后文再進(jìn)行討論，在此先分析不定式的邏輯主語。
（2） for sb. to do
不定式的邏輯主語常見的是由“for + 名詞 / 代詞”引出，這里的“名詞 / 代詞”即是不定式的邏輯主語，來說明不定式動作的執(zhí)行者。
a.It's important for you to go there in person.
你有必要親自去那兒一趟。
b.It is very common for him to be absent without leave.
不請假就擅自離開是他的一貫作風(fēng)。
c.He was very willing for everyone else to come.
他很愿意讓其他所有的人都來。
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.
對于任何黏合劑，要想粘得牢固的話，則被粘的表面必須絕對清潔且不能潮濕和有油性物質(zhì)。
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.
下列句子因為不定式的邏輯主語不明確而顯得不規(guī)范，因此在寫作文時要避免。
g.To study English well, a lot of practices are needed.*
h.A lot of practices are needed to study English well.*
g，h兩句要表達(dá)的意思是：“要想學(xué)好英文，大量練習(xí)是必要的。”但完全是受漢語思維影響而寫出的句子。
以上兩句均因句子主語a lot of practices不能作不定式to study的邏輯主語而顯得不規(guī)范。因此，上面兩句可以改為：
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
用來說明人的性格特征或行為表現(xiàn)的動態(tài)形容詞與不定式連用時，用“of +名詞 / 代詞”這一結(jié)構(gòu)引出不定式的邏輯主語。這樣的形容詞主要有：
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的使用規(guī)律是：看句中的表語形容詞是著重說明人（邏輯主語）還是事（不定式短語）。若是前者，則用of；若是后者，則用for。另外，用of的句子，可以用人作主語將句子改寫，用for的句子則不能。試比較：
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.（邏輯關(guān)系正確）
g.It's wise of you not to argue with your boss.