连接词
（1）表选择关系或对等关系的连接词：either…or…,neither…nor, or, as well as…, and, both…and….
（2）表因果关系或对等关系的连接词：therefore, so, as a result, as the result of …,because of, due to …,owing to, thanks to等.
（3）表时间顺序的连接词：the moment, as soon as, at first, then, later, meanwhyle, at the beginning, in the end, before long, for the first（second…）time, the minute等.
（4）表转折关系的连接词：yet, and yet, but , while, on the contrary, on the other hand, however, at the same time（然而）等.
（5）表解释说明的连接词：that is, that is to say, in other words, such as, for instance, and so on, etc. and the like等.
（6）表递进关系的连接词：not only…but (also), what,s more, what's worse, besides, in addition, worse still, moreover, above all等.
（7）表示总结的连接词：in a word, on the whole, in short, briefly, in brief, to sum up, in all等.
所以 so为因果关系连接词,then为时间顺序连接词
另外,如果按连词分类为从属连词和并列连词的话,so和then都为并列连词
参考资料:http://zhidao.baidu.com/question/174180180.html
