我們學習英文文法，在名詞(noun)之後，一定會學到代名詞(pronoun)，其中之一是 it. 查英漢字典，it的解釋是：(文法)「虛字」(expletive)，在句子結構上是必要的、但却是無意義的字。文法上it稱為代名詞，代替動物或事物。當它用在句子當中的時候，它本身並不具備任何意義，所以我們才會稱它為「虛字」。
it在句子中的十一種用法如下：
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| 1. |
It is three o’clock now. (time, It 代替時間) |
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| 2. |
It is rather hot today. (weather, It 代替天氣) |
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| 3. |
It is about five miles from my home to the university.
(space, distance, It代替空間、距離) |
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| 4. |
I bought a dog yesterday. I like it.
(It refers to a dog)
(It是代名詞，代替動物a dog「狗」) |
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| 5. |
When we have lost our health, we value it most.
(It is a pronoun, and it refers to our health.)
(It是代名詞，代替事 "our health.") |
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| 6. |
It is difficult to write English.
(It represents the real subject to write English / appositive—subject.)
(to write English在文法上稱為infinitive phrase, 即不定詞片語)
(It代替真主詞to write English.)
(to write English也稱為虛主詞It的同位語)
(亦可以寫作To write English is difficult.) |
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| 7. |
Our teacher makes it a requirement to prepare lessons beforehand. (It represents the real object to prepare lessons beforehand /
appositive—object.)
(it代替真受詞to prepare lessons beforehand.)
(to prepare lessons beforehand在文法上稱為infinitive phrase, 即不定詞片語)
(to prepare lessons beforehand也稱為虛受詞it的同位語.) |
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| 8. |
It is difficult for me to write English.
(It represents the real subject for me to write English / appositive—subject)
(It 代替真主詞for me to write English)
(for me to write English 在文法上稱為infinitive clause, 即不定詞子句，雖然它並不具備子句的條件)
(for me to write English 也稱為虛主詞it的同位語.) |
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| 9. |
It is true that he is a good student.
(It represents the real subject that he is a good student / appositive—subject)
(It代替真主詞that he is a good student)
(that he is a good student是名詞子句)
(that he is a good student 也稱為虛主詞it的同位語)
(亦可改寫為That he is a good student is true.) |
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| 10. |
It was I thatstarted the quarrel.
("It be . . . that…. " is used to emphasize the subject,
即加强句中主詞I.)
(I started the quarrel. 即非加强句) |
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| 11. |
It was Bert that I met at a bus station in Taipei City.
("It be . . . that…. " is used to emphasize the object,
即加强句中受詞Bert.)
(I met Bert at a bus station. 即非加强句) |
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※ 詳見 實用英文文法與修辭(九版六刷)
(原文出自金陵英語教學網，原文網址http://www.ep66.com.tw/use-of-it.htm) |
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