有語法基礎(chǔ)的同學(xué)都知道，英語句子除祈使句 (imperatives) 外，都要有主語。

有些句子的主語非常奇怪，叫“假主語”（或形式主語），因?yàn)檎嬲闹髡Z非常長(zhǎng)，為了避免頭重腳輕，需要放在句中或句末。

這種假主語的英文叫 preparatory subjects 或 dummy subjects（dummy 這個(gè)詞用得很形象）。

英文所用的假主語有二：There 和 it。

There 在 There is (There’s) 和 There are 結(jié)構(gòu)中是當(dāng)作假主語，真正主語是 There is 或 There are 后面的名詞或名詞短語。

There’s a girl on the phone for you. (有個(gè)女生打電話找你)

這句的 There 是假主語，真正主語是 a girl。

It 在句中當(dāng)假主語時(shí)，真正主語有三種型態(tài)：不定式主語、動(dòng)名詞、以及 that 從句。例如：

It’s very hard to believe that he is an honest employee. （很難相信他是個(gè)誠(chéng)實(shí)的員工。）

這句的 It 是假主語，真正主語是不定式短語——to believe that he is an honest employee。

如果按常規(guī)語序，這句可改成 To believe that he is an honest employee is very hard.。

再來：

It’s worth calling him to clear up the misunderstanding between you and him. （值得打電話給他澄清你和他之間的誤會(huì)。）

這句的 It 是假主語，真正主語是動(dòng)名詞短語——calling him to clear up the misunderstanding between you and him

按常規(guī)語序是 Calling him to clear up the misunderstanding between you and him is worthwhile.。

再來：

It is difficult (that) they would finish their work in two days. （他們要在兩天內(nèi)完成工作是有困難的。）

這句的 It 是假主語，真正主語是that 引導(dǎo)的名詞短語—— that they would finish their work in two days。

所以，若按常規(guī)語序，這句要寫成：That they would finish their work in two days is difficult.

對(duì)了，如果真正主語 (即 that 所引導(dǎo)的名詞從句) 置于句首，則 that 不能省略。