therefore有兩種用法,一在整句中,一在分句中.therefore是副詞,但有時具有連詞作用。
一、整句中時一般不放句末,句首后要有逗號,句中1、按一般副詞使用2、做插入語
例句：
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，即一個句子一部分表示原因一部分表示結果。
這時一般詞前要用分號,其后用不用逗號無所謂。若第二個分句前是逗號或無符號，則要注意therefore是副詞，和so不一樣,要保持句子完整，應用and therefore。
例句：
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.