1.so可以用作连词，表示“因此，所以”。

　　例：I heard some noise outside, so I went out of the room to see why.

　　so that作为连词词组，表示 “以便，为了”。

　　例：The vase is put high on the table, so that it won’t be broken.

　　2.so可以用作形容词，表示“是这样的，是真的”。

　　例：The newspapers claim she killed him in self defence but that just isn’t so.

　　3.so可以用作副词，表示——

　　1)“如此，这么”结构为：so+adj./adv

　　例：She was so tired that she fell asleep very fast.

　　表示此意思时，还可以用：so+adj.+a/an+n.

　　例：It is so good a movie that everyone who saw it praises it very much.

　　2)“如此，如是”，用于表示已经提到的想法，建议或情况等

　　例：“Will I need my umbrella?”

　　“I think so.”