(1) The Internet will not only make it easier to keep up with distant friends, … (Passage A, Unit 10)
(2) It is natural that friendships formed across the Internet will lead to getting together in person. (Passage A, Unit 10)
可以看出，上面两句话的词序都经过了一番调整。未调整前的词序分别是：
(1) The Internet will not only make to keep up with distant friends easier, …
(2) That friendships formed across the Internet will lead to getting together in person is natural.
英语的词序 (word order) 是指各句子成分在句中的前后次序，一般情况下是主语 (S) — 动词 (V) — 宾语 (O) —宾语补足语 (Co)或状语 (A) 等。但有时为了交际或文体上的需要，说话者会对词序进行调整。上面两例中的词序调整都遵循了同一个原则，即将句中最长或最复杂的成分移至句末，以避免头重脚轻。这一原则在英语语法中被称为末尾重心原则 (the principle of end-weight)。
通过调整词序或转换句型获得末尾重心的效果，一般有以下几种途径：
1. 形式主语
当主语是一个较长或较复杂的不定式短语、-ing分词短语或名词分句时，通常用it作形式主语，而把真正的主语移至句末，如上例（2）。又如：
It is important for the students to have a deeper understanding of the texts.
It makes no sense to read the article word for word from the beginning to the end.
It is necessary to speed up and finish the work earlier.
It will be a waste of money to buy such an expensive and useless thing.
It is easier talking than doing.
It’s no use telling that to everybody.
It’s fun acting in a film.
It is probable that she will come to the party tonight.
It was obvious that the driver could not control the car.
It isn’t surprising that he should have said that.
It doesn’t matter that he has changed his plan.
Isn’t it strange that he is wearing so much in such a hot day?
2. 形式宾语
在SVOCo (即“主语+动词+宾语+宾语补足语”) 句型中，如果宾语是一个较长或较复杂的不定式短语、-ing分词短语或名词分句，而宾语补足语又较短，通常用it充当形式宾语，而把真正的宾语移至句末，如上例(1)。又如：
He thought it right to believe what I had told him.
I made it my business to translate the letters.
You must find it exciting working here.
He found it dangerous climbing up the mountain.
He finds it necessary that a teacher respect and love his students.
We thought it interesting that everyone wore the same type of shoes.
I find it possible that he came yesterday but didn’t meet us.
The officer found it important that everybody should keep it a secret.
The teacher made it clear that we had to hand in our homework today.
3. 宾语与状语倒置
在SVOA (即“主语+动词+宾语+状语”)句型中，如果宾语较长或较复杂，而状语又较短，通常将宾语和状语倒置，使宾语处于句子末尾。例如：
He said to me that he didn’t agree with Bob.
We heard from his own lips the story that he had nearly been killed by a car.
I read eagerly the book written by that famous British writer.
The doctor examined with great care the patient who had been sent to hospital ten minutes ago.
The man said with deep feelings that he still loved her after so many years.
She sang sadly the song her mother taught her when she was a child.
除上述三种途径外，还有其他一些方式也可以通过调整词序获得末尾重心的效果，比如直接宾语和间接宾语的互换（如下例1和2）、主动语态和被动语态的互换（如下例3和4）等：
(1) He told his mother the truth that he had stolen her money.
(2) He told the truth to his mother, who was in the last minutes of her life.
(3) Tom beat Mark, who had won the game three times.
(4) Mark was beaten by Tom, who had never won the game.
末尾重心语法原则
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