I'd better为啥是I had better? 怎么像个语法错误?

最早，古英语有me were betere这个用法，其中me不是现代英语的宾格，而是古英语中的“与格（dative case）”，相当于德语语法的“第三格（Dativ）”

到了中古英语，me were betere的与格被改成了主格I，即I were better（betere也随着中古英语的变化变为了better）。

16世纪时，I were better受到另一个短语I had rather（现已基本被I would rather取代）的影响改为了现在流行的I had better了