【问】 下面是《大学英语四级考试常见错误分析》(P.33)对for和because的正误分析：
 “误：The day breaks because the birds are singing.
 正：The day breaks for the birds are singing.
 译：天亮了，因为鸟在叫。
 析：because表示真正的原因，因为鸟叫不是天亮的原因，要日出才能破晓，所以只能说：The day breaks because the sun is rising.鸟叫不是天亮的原因，而是结果。鸟之所以叫，其理由是天亮了。这种倒果为因的说法，英文只能用for，eg：It is going to rain，forthe barometer is falling.(天要下雨了，因为晴雨计正在下降。)
 误：The river has risen，for it has rained much of late.
 正：The river has risen，because it has rained much of late.
 译：河水涨了，因为近来下了许多的雨。
 析：because指的是道德的或自然的原因(moral or physical cause)，而for则指的是逻辑上的理由(logical reason)。请看下例：It must have rained much of late，for the river is sohigh.(近来一定下了许多雨，因为河水涨得这样高。)这句谈的是理由。”
 下面是《英语疑难大全》(天津大学出版社，P.534)对for和because用法的分析：
 “如果从句并不表示原因，而只是为主句中所说的话提供推断的理由加以解释时，从句只可用for引导，且for前常有逗号。
 误：He must be at home because(as，since) the light in his room is on.
 正：He must be at home，for the light in his room is on.
 房子里的灯是开着的，并不是他在家的原因，而只是为证明他在家提供的一个推断的理由。”
 读了上面的说明，我产生一个问题：难道for只能用来表示“由for分句所表示的结果推断出前一个分句所表示的原因”吗? for分句难道就不能表示原因吗?如果不能表示
 原因，那如何解释下面的句子?
 The days were short，for it was now December. (PEG)
 能否说for it was now December是结果，而the days were short是原因呢?
 【答】 以上两本书清楚地解释了for的一种用法以及它与because的区别。上面的讲法对于英语初学者是适当的。但是，英语水平较高的读者应进一步了解：连词for也可以表示原因或理由，请看下面的实例：
 1. She’s gone for a walk，for the rain has stopped. (CGEL)
 她出去散步去了，因为雨停了。
 2. She’s gone for a walk，because the rain has stopped. (CGEL)
 她出去散步去了，因为雨停了。
 3. Even in his irritability he was gentle，for Leora was with child.(Lewis)
 甚至在他烦躁时，他也显得很温和，因为利奥拉怀孕了。
 4. She was angry，for she didn’ t know French (here for is correct; beacuse is alsopossible). (PEG)
 她生气了，因为她不懂法语。
 5. We must start early; for we have a long way to go. (LDCE)
 我们得早点动身;因为我们必须走很远的路。
 6. I must be off now，for my sister is expecting me. (PEG2)
 我得走了，因为我姐姐在等我。
 7. This would solve the problem of ventilation，for if a train entered this tunnel，it woulddraw in fresh air behind it. (NCE 2，L. 64)
 这样就可以解决通风问题，因为如果火车开进隧道，它后面就会带进新鲜空气。
 请做下面的英语试题：
 1. Someone must have left the tap on，____the water was running over and flooding thebedroom.
 A. therefore B. for
 C. nevertheless D. moreover(攻读硕士学位研究生入学考试英语试题，84A)
 2. Neon is said to be inert____does not react easily with other substances.
 A. because of it B. because it
 C. it is because D. is because it(TOEFL，87. 5)