三、 表達原因的結構
考生病句：
1. The real reason to our failure is not far to seek.
2. The reason for this is because some people want to earn plenty of money without working hard.
正確表達：
1. The real reason for our failure is not far to seek.
2. The reason for this is that some people want to earn plenty of money without working hard.
評議與分析：
以上兩個病句分別引自92年1月和97年12月四級考試的考生作文。從遣詞造句上看，這兩位考生具有一定的寫作能力，not far to seek, plenty of money以及without working hard等均運用正確、恰當。但令人遺憾的是，第一位考生不知道reason不與to搭配而應接介詞for，第二位考生犯了一個中國學生常犯的錯誤，就是用because引起表語從句，because這個詞不能引起表語從句，在本句中只能改用that才正確。
掌握好表達原因的結構是十分重要的，幾乎所有的寫作試題都要求寫原因或可以寫原因。在大學英語四、六級考試、研究生入學英語考試以及TOEFL考試中，寫作的文體基本上是議論文，而議論文的基本模式是擺事實、講道理，講道理就是說明原因。寫作測試的文體決定了表達原因結構的重要性。
英語中用來表達原因這一概念的結構有多種。我們可用as , because, since, seeing that, considering that, now that, not that...等詞組引出表示原因的從句。例如：
1. Now that we have seen these great achievements with our own eyes, we feel more proud than ever of our country.
2. Professor Liu is strict with us because he wants us to make rapid progress.
3. Since we live near the sea, we enjoy a healthy climate.
4. Pollution is still a serious problem, not that we don't have the ability to solve it, but that some people have not realized the consequences of the problem.
我們還可以借助某些詞語用簡單句表達原因結構。例如：
1. The reason for this change is quite obvious.
2. Diligence is the key factor of success.
3. Idleness is the root of all evils.
4. He was ashamed to have made the mistake.(=He was ashamed that he had made the mistake. =He was ashamed because he had made the mistake.)
除了上述的例句外，英語中還有很多或易或難的表達原因的結構。我們在進行寫作訓練的時候，不能滿足于一知半解，要講究書面語言的正確性和準確性。比如，because是最常用的引導原因從句的連詞，語氣最強，表示直接的原因，若because置于句首，后面的主句不能再用so。用as引導的原因從句語氣較弱，所說明的原因是附帶的，而since表示的原因暗示著是稍加分析之后才能推斷出來的原因。
四、 否定結構
考生病句
1. Some people think we needn't to worry about fresh water.
2. Nowadays many people don't like to go to the movies, too.
正確表達：
1. Some people think we needn't worry (或don't need to worry) about fresh water.
2. Nowadays many people don't like to go to the movies, either.
評議與分析：
例句1選自96年1月四級考生作文，例句2選自92年1月六級考生作文。例句1 的錯誤在于該考生混淆了need作為情態動詞和作為普通動詞的用法。
need作為情態動詞時，主要用于否定句，后面的動詞不帶to, needn't worry，作we的謂語。need作為實意動詞時，可用于肯定句、否定句和疑問句，don't need to worry 中的to worry作don't need的賓語。例句2的錯誤在于該考生混淆了too和either的區別，這兩個詞都表示"也"的意思，但是在英語中too, also只能用于肯定句，而either只能用于否定句。
否定結構除了在助動詞、情態動詞，be和have后面加not之外，還有許多不含not的否定結構。若能正確使用他們，文章會顯得生動活潑，增加寫作的閃光點。下面我們就來看看:
1． 含有否定意義的詞匯和短語
以下列舉的詞和詞組本身就具有否定的含義，因此無需用否定詞。
介詞against, beyond, but, except, without,...
形容詞和動詞absent, deny, differ, different, fail, free, ignore, miss, refuse, the last, used to, reluctant, lack, want,...
短語keep...from, protect...from, prevent...from, let alone, at a loss, in vain, instead of, out of the question, rather than, too...to, by no means, anything but,...
我們看以下例句：
1） Women fail to get the equal rights in some countries.
在一些國家里婦女沒有得到平等的權利。
2） This is by no means the best way to solve the problem of energy crisis.
這不是解決能源危機的最好的辦法。
3） We should protect trees from being destroyed.
我們應保護樹木，不讓它們受破壞。
4） In old China we could not make a nail, let alone(make) machines.
在舊中國，我們連一個釘子都造不了，更不用說制造機器了。
2． 含有半否定意義的詞語
barely, hardly, few, little, rarely, scarcely, seldom, not all, not everyone, not everything,...具有半否定的意義。例句：
1） We could hardly see any fresh vegetables in winter on market several years ago.
幾年前在冬天市場上很難見到新鮮蔬菜。
2） These young people know little about how to choose good books to read.
這些年輕人幾乎不知道如何挑選優秀的書籍來讀。
3． 不含否定意義的否定結構
有些詞和詞組形式上是否定結構，但其含義是肯定的，比如：cannot but, can't help, no sooner...than, not...until, in no time, none other than, nothing but,等等。例句：
1） We can't but face the reality.
我們只有面對現實。
2） These old buildings will be replaced by modern apartment buildings in no time.
這些舊建筑將很快為現代化的公寓所代替�！ �
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