核心问题
He ran away from school. He ought to have known better. 请问句中的 know better 是什么意思？应如何翻译？
词典解答
know better 一般可理解为 know better than to do sth. 的省略形式。因此，上面的句子 ... have known better 可以理解为 ... have known better than to run away from school (to do so)。全句似可译为：他逃学了。他本应该懂得不该这么做的（他本应该更懂事一些的）。（参见 know better than to do）
有时候, know better 是一个独立的用语, 而并非是 know better than to do 的省略形式: The experts, who knew better, laughed at the idea. (EED) 专家们更加敏锐, 嘲笑了这种想法。