一般情況下不定式作主語都要用it作形式主語來代替的.
Ⅰ.動名詞和不定式做主語的相同點
1.不定式短語和動名詞做主語時,常常為了保持句子的平衡,用it來做形式主語,如：
It is not easy to learn English well.
It is no use asking him for help.
2.如果主語用了不定式,表語和賓語也要用不定式;主語用了動名詞,表語和賓語也要用動名詞,這在英語中稱為對稱性,如:
To see is to believe.= Seeing is believing.(眼見為實)
(85)It is better to stay home than _A__ out.
A.to go B.going C.go D.gone
Ⅱ.動名詞和不定式做主語的不同點
1.不定式做主語常表示具體的某一動作;表示泛指或一般的抽象的概念時,多用動名詞,如:
(92)_B_ is a good form of exercise for both young and old.
A.The walk B.Walking C.To walk D.Walk
2.在”There/It +be+ no use(good/help/need)”之后常用動名詞做主語,而少用不定式,如:
It /There is no use crying over the split milk.
It /There is no help taking this medicine.
★但是如果該句型中用了for引出不定式的邏輯主語,就只能用不定式,如:
(93) There is no good for us to do that exercise.
3.不定式可以和when,where,how,what,whether等連用,在句子中做主語,賓語和表語,而動名詞則不能,如:
How to solve the problem is a hot potato.
Where to put the box seems hard to decide.
Whether to do it hasn’t been decided.
What to do next is up to you.那請問不定式作主語為什么要用it作形式主語來代替呢？？說實話，這個我還真不知道！我覺得應(yīng)該是跟it的作用有關(guān)系吧！一般情況下不明的東西都可以用it來說明。比如說打電話的時候會說：who is this speaking? 回答者就可以說：it is john 等等！你問我的這個問題就相當(dāng)于這樣的！為什么在英語中“他”要翻譯成He呢？希望你可以理解我的回答！