might在语法形式上，是may的过去式。所以，如果要表达对现在或未来的猜测的话，一般要用may而要表达对过去的猜测的话，则要用might。
①一般来说，may所表达的可能性比might要更大。
如：
They may visit Ireland in the near future.
这句话说明说话者认为他们还是比较有可能在不久的将来去爱尔兰的。
The woman looked as if she might have been in her late 40s.
这句话说明说话者并没有什么把握确定这位女士的年龄，只是做了个尝试性的猜测而已。
需要注意的是，如果只是做假设性的猜测的话，还是建议多用might。如果是在虚拟语气中，肯定要用might。
如：
If I were Dutch Imightsee immigration differently.
If you go to bed earlier， you might feel better tomorrow.
②如果要提出问题、请求或建议时，might比may更加礼貌、委婉。
如：
Don't you think you mightbe a little old for him?
MightI ask the Court to glance briefly at the judgment of Sir Harry Gibbs?
③在间接引语中，may要改为might。如：
直接引语：She said，“I may go out of business.'
间接引语：She said she might go out of business.
