回答http://www.yygrammar.com/Article/201403/3568.html

http://blog.163.com/ki_kihappy@yeah/blog/static/1704886632010910112834700/

therefore 

therefore有两种用法，一在整句中，一在分句中。
一、整句中时一般不放句末，句首后要有逗号，句中1、按一般副词使用2、做插入语（这两个分得清吧）
eg.1、Therefore，we must learn English well.
   2、They therefore can learn English well.
   3、Many fast food restaurant ,therefore,have red furniture or walls.
二、用在分句中，即一个句子一部分表示原因一部分表示结果。
这时一般词前要用分号，其后用不用逗号无所谓。若第二个分句前是逗号或无符号，则要注意therefore是副词，和so不一样，要保持句子完整，应用and therefore。
eg.1、I had a headache;therefore I could not go to your party.
   2、I was ill,and therefore could not come.
   3、These birds are very beautiful and therefore liked by many people.

注：therefore是副词，但有时具有连词作用

 

therefore，otherwise 和 thus 的区别

Therefore要加逗号，后面跟句子（注意是句子）；
Thus不一定要加逗号，后面不一定跟句子。

I was helping my sister with her study.Therefore,I failed to pass the exam.

Air carry the virus to everywhere,thus causing the explosion of the disease.（无逗号，thus 后面不是句子）
Air carry the virus to everywhere.Thus,it causes the explosion of the disease.（逗号，thus 后面是句子） 



用于句型“祈使句+or+陈述句”中，表示在以祈使句为条件下的相反假设，意为“否则，要不然”。

例如： Work hard,or you will fall behind.你要努力学习，否则会落后。

 Get up early tomorrow,or you will miss the early train.你明天要早点起身，要不然就赶不上早班火车了。

Don't jump the queue,or other peopoe will not be pleased.别插队，否则别人会不高兴的。

可以把这类句型中的祈使句换为一个条件句（注意改写时应去掉连词or）。

例如： Hurry up,or you will be late for the meeting.→If you don't hurry up,you will be late for the meeting.

otherwise 用作连词，意思为“否则；要不然”，相当于 or，or else 或 if not .  

例如：  We’ll go early，otherwise we may not get a seat.  我们得早点去，要不然就没有座位了。 

Seize the chance，otherwise you will regret it.  抓住机会，要不然你会后悔的。 

 I was ill that day，otherwise I would have taken part in the sports meet.  那天我病了，否则我会去参加运动会的。

  We didn’t know you were in trouble at that time，otherwise we would have given you a hand.  我们当时不知道你遇到了困难，要不然我们会帮助你的

 

because、for、therefore作“因为”讲的区别

for ,because,as,since这四个词作为连词，都有"因为"的意思，但它们在用法上有区别： 


because 是从属连词，接表示直接原因的从句，一般放在主句的后面，也可放在主句前面，它表示的语气最强，在回答why的问句时，必须用because。 

例如：The swimming pool won't be open today because they're making repairs. 

游泳池今天不开放，因为他们在修理。 

Why did you move to France? 

你们为什么搬到法国？ 

Because my father found work in Paris. 

因为我父亲在巴黎找到了工作。 

注意：在英语中用了because后，不可再用so。 


as 是从属连词，说明一般的因果关系，语气比because弱，说明比较明显的原因，它引导的从句通常放在句首，有时也可放在句末。 

例如：As it is raining, you\'d better take a taxi. 

天下雨了，你最好乘出租车。 


since 意为"既然"，表示对方已知的无需加以说明的原因或事实，语气比because弱，但是比as 强。 

例如：Since we have no money, we can't buy that vase. 

既然我们没钱，我们就不能买那花瓶。 

Since everybody is here, let's begin our party. 

既然大家都到了，那就开始我们的聚会吧！ 


for 是并列连词，用来附带解释说明前一分句的原因或理由，for引导的并列句，一般放在所要说明的句子的后面。 

例如：I went to see him, for I had something to tell him. 

我去见他，因为我有事要告诉他。 

只有therefore是表示结果的意思而不是原因.

 

Therefore，Thus ，hence，then，accordingly与So用法辨析

1.therefore adv.因此, 所以=for that reason=consequently常用于连接两个并列分句，其前加“and”或分号“；”。

• He was ill, and therefore could not come. 他病了, 所以未能来。
• He has broken his leg and therefore he can't walk.他摔坏了腿，因此不能走路了。
• We do not have enough money. Therefore we cannot afford to buy the new car.我们的钱不够,因此买不成这辆新车。

2、so conj. adv因而, 所以, 结果是

• It was late, so we went home. 天晚了, 所以我们就回家去了。
• He was sick, so they were quiet.他病了，所以他们很安静。

3、hence adv.因此, 从此

• The town was built among the hills, hence the name Hilltown. 该城镇修建在群山之中,故取名'山城'。
• It is very late; hence you must go to bed.时间已经很晚了，因此你必须睡觉去。（记住前面是分号，而不是逗号）

4、then adv因此，就

  Go into the cave, then they won't see you. 躲进洞里去，那他们就看不到你了。

5、accordingly adv.因此, 从而；所以，因此结果；因此（偶作连词使用conj.）

• He was asked to leave the city and accordingly he went.有人叫他离开该城市,所以他就走了。
• You may arrange accordingly.你可以权宜处理。
• Mr Foster has never been to China. Consequently / Hence he knows very little about it.福斯特先生从未去过中国,所以对中国了解得很少。
• My car was broken down and consequently I was late. = in consequence

6、Thus  adv.如此，像这样；因此；于是

• He sold his farm and thus he had enough money for his journey.他卖掉了农场，这样他就有足够的钱旅行了。
• There has been no rain — thus, the crops are drying.天没下雨，因此庄稼要枯死了。