1. because (conj.) / because of (prep.)
because 可以说是因果关系句型中最常见的字了，because 是从属连接词，后面要加上一个完整句子，也就是有主词、动词的句子。 because 加上了 of 之后变成了介系词，后面必须要加上一个名词或是动名词，才是正确的。
He did very well on the mid-term exam because he studied hard for it.
他期中考考得很好，因为他很用功地念书。
The window of the office was broken because of the continual strong wind.
由于接连的强风，办公室的玻璃破了。
2. due to (prep.)
due to 是个介系词，后面必须要加上名词，不可以接完整句子。
(O) His failure was due to his arrogance.
他的失败是因为他的骄傲。
(X) His failure is due to he is too arrogant.
他的失败是因为他的骄傲。
3. because of 和 due to 到底哪里不一样？
because of 和 due to 两个词虽然在中文可能都会翻成「因为」，词性也都是介系词，但是其实他们的用法却是不一样的，不可以随便替换，会造成文法错误！
because of 前面必须是有一般动词的完整句子，而 due to 前要有名词，不能是一般动词（be 动词不是一般动词，be 动词是 linking verb，中文有时会翻成系词），因为 due to 本质上是用来说明、形容名词的。
(O) He got sick because of a sudden drop of the temperature.
(X) He got sick due to a sudden drop of the temperature.
因为气温骤降，他生病了。
(O) The company’s huge success is due to the team’s hard work.
(X) The company’s huge success is because of the team’s hard work.
这间公司的伟大成功，是因为团队的努力工作。
4. owing to (prep.)
owing to 和 because of 词性一样，都是介系词，且用法一样，只能用在有一般动词的完整句子后面。
(O) He fell asleep as soon as he laid down owing to a lack of sleep.
他因为缺乏睡眠，一躺下去就睡着了。
(X) His fatigue is owing to a lack of sleep.
他的疲惫是因为缺乏睡眠。
比较：
(O) His fatigue is due to a lack of sleep.
他的疲惫是因为缺乏睡眠。
5. since (conj.)
since 不只表达原因，里面还暗藏了「既然」的口气。
Since you are here, could you help me move this heavy box?
你在这里，你可以帮我搬这个重箱子吗?
比较：since (prep.)
since 也很常被拿来当作介系词用，意思是「自从」后面要加上一个过去事件或是时间点。
He has lived in San Francisco since 1987.
他自从1987年就住在旧金山了。
He has been depressed since his wife passed away.
自从他的妻子过世后，他就一直很沮丧。
6. for (conj.)
for 当「因为」时是连接词，一般而言是表示推测的原因，后面加上完整句子，记得 for 前面要加上一个逗点。
They remain silent, for they don’t know what to say.
保持沉默，因为他们不知道要说什么。
It must have just rained, for the ground is wet.
刚刚一定才下完雨，因为地上湿湿的。
