therefore的用法以及與because、for的區(qū)別

　　therefore有兩種用法,一在整句中,一在分句中.therefore是副詞,但有時(shí)具有連詞作用.

　　一、整句中時(shí)一般不放句末,句首后要有逗號(hào),句中1、按一般副詞使用2、做插入語(yǔ)(這兩個(gè)分得清吧)

　　eg.

　　1、They therefore can learn English well.

　　2、Therefore,we must learn English well.

　　3、Many fast food restaurant ,therefore,have red furniture or walls.

　　二、用在分句中,即一個(gè)句子一部分表示原因一部分表示結(jié)果.

　　這時(shí)一般詞前要用分號(hào),其后用不用逗號(hào)無(wú)所謂.若第二個(gè)分句前是逗號(hào)或無(wú)符號(hào),則要注意therefore是副詞,和so不一樣,要保持句子完整,應(yīng)用and therefore.

　　eg.

　　1、I was ill,and therefore could not come.

　　2、I had a headache;therefore I could not go to your party.

　　3、These birds are very beautiful and therefore liked by many people.

　　注：therefore是副詞，但有時(shí)具有連詞作用

　　therefore，otherwise 和 thus 的區(qū)別

　　Therefore要加逗號(hào)，后面跟句子(注意是句子);

　　Thus不一定要加逗號(hào)，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.(無(wú)逗號(hào)，thus 后面不是句子)

　　Air carry the virus to everywhere.Thus,it causes the explosion of the disease.(逗號(hào)，thus 后面是句子)

　　用于句型“祈使句+or+陳述句”中，表示在以祈使句為條件下的相反假設(shè)，意為“否則，要不然”。

　　例如： Work hard,or you will fall behind.你要努力學(xué)習(xí)，否則會(huì)落后。