有一读者问：because, since, for, because of, on account of 有什么区别？
because 和 since 意指“因为”时都是从属连词，because 表示直接理由，常用以回答 why，语气较强，实例如：
(1)I can't go, because I'm busy.
(2)Because no one tended the trees, a large number died.
注意上述句（2）可变为强调结构如下：
(3)It was because no one tended the trees that a large number died.（强调结构中的 because 不可代之以 since 或 as）
since 常相当于汉语的“既然”，其语气弱于 because，实例如：
(4)Since we've got a few minutes to wait for the train, let's have a cup of coffee.
注意有时并不能译作“既然”，如：
(5)Aircraft noise is a particular problem here since we're close to the airport.（since 在此可代之以 as）
顺便提一下，从属连词 as 亦可表示“因为”，但其语气更弱，常有其所表的原因或理由较为明显的含义，实例如：
(6)As he was not feeling well, he had to stay at home.
(7)I am going to bed, as I'm very tired.
for 亦可意指“因为”，但它不是从属连词，而是一等立连词，常用以表示上文未提到的附加的或补充性的理由，其前常有一逗号，实例如：
(8)It will rain, for the barometer is falling.（注意此处的 for 不可代之以表直接理由的 because）
for 表示补充性理由时可放在括号之中，如：
(9)The old man raked the fire together with an old stair-rod, and having trimmed his smoky lamp （for it was night）, with the stem of his pipe, put it into his mouth again.
for 还可引导一个独立句甚至一个段落，如：
(10)For , you see, they trusted their own sense of touch very much.（摘自The Blind Men and the Elephant ， for 引导独立句）
(11)For whatever the outcome of that game, the Koreans will be the champions.（摘自China Daily ,for 引导一个段落）
for 还可用作介词，意指“由于”，较为正式，常用以表示感情、赏罚等，实例如：
(12)He shouted for joy.
(13)He was rewarded for saving the girl's life.
(14)The driver was punished for the accident.
注意下列一类的常见搭配：
(15)Maxie Curie is famous for her contribution to science.（famous for 是常见搭配）
(16)You cannot see the wood for the trees.（for 常与 cannot ... 搭配）
because of 与 on account of 都是短语介词，意为“由于”，但后者似乎常用于正式文体中，试比较：
(17)He did not come to school because of illness.
(18)He was absent from school on account of illness.
