(1)表示选择关系的连词，连接的双方只取其一。常用连词有or, either...or, otherwise
例如：
1)You can go to Beijing either today or tomorrow
2)You must get up early or you won't catch the early bus.
(2)表示转折关系，连接的双方构成对比，意义上有转折。常用连词有but, however, while, only
例如：
1) His brother is fond of football while he likes basketball.
2) You can watch TV, but you must finish your homework first.
(3)表示联合关系，联合的双方是对等的，意义上趋向一致。常用连词有：and, both...and, neither...nor, not only...but also, as well as, together with
例如：
1) To study English well, we need both diligence and careful.
2) That horse is not only the youngest among the five, but also runs the fastest.
(4)表示因果关系，连接的双方，互为因果，或者前因后果，或者前果后因。常用的连词有：for, so, therefore
例如：
1) It must have rained, for the ground is wet.
2) You are in the right, therefore they should support you.