had better表示最好

had better 相当于一个助动词，它只有一种形式，它后面要跟动词原形。

　　had better do sth

上海龙凤1314 shlf　　had better not do sth

　　It is pretty cold. You'd better put on my coat.

上海龙凤1314 shlf　　She'd better not play with the dog.

　　had better have done sth表示与事实相反的结果，意为"本来最好"。

上海龙凤1314 shlf　　You had better have come earlier.