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。来源:考试大 had better do sth had better not do sth来源:考试大 It is pretty cold. You d better put on my coat. She d better not play with the dog. 来源:考试大
had better have done sth表示与事实相反的结果,意为"本来最好"。 You had better have come earlier.