主要區(qū)別如下：
1.用于疑問句表示請求時,一般只用Could,且可用于各人稱.如：
Could you help me explain the difference between "might" and "could"?
Could I use your mobile phone a little while?
上句可用May代替：May I use your mobile phone a little while?
用Might也是可以的,但不常見.
2.could和might都可用在條件句中,表示假想的情況.表示“本來會、本來可以/能夠”.例如：
If you tried you could/might do the work better.如果你試試的話,準(zhǔn)能把那項(xiàng)工作干得更好.
You could have met her if you had gone that way.如果你走那條路的話,你準(zhǔn)能遇見她.
此句中的could如改成might則表示：……,你也許能見到他.
They could/might have worked it out if they had asked me for help.如果他們來向我求助的話,他們本能夠做出來的.
He could/might have give the answer,but he refused to.他本來能夠回答的,但他拒絕這么做.
You were stupid to go skiing there — you could have broken your leg.你真笨,竟會到那地方滑雪.你本來會摔斷腿的.
上面的例句中用might則因其語氣較輕而語意效果不甚理想.
在此場合,could和might的區(qū)別是could較might的可能性強(qiáng).
3.couldn't be + 比較級句型不能用might代替.如：
Their lifestyles couldn't be more different.他們的生活方式極為不同.
4.could和might都可用在表示“結(jié)果”的狀語從句中,同樣,could語氣較重些.例如：
He expressed his ideas clearly so that the average person might understand.他把他的意思清楚地表達(dá)出來,以便一般人能聽明白.
5.might as well表示“不妨、可以、倒不如”,此時的might是不能用could代替的.例如：
We might as well look for some food now.現(xiàn)在我們不妨找些吃的東西.
I expect I might as well be going.我希望我可以走了.
Since it’s a fine day we might as well walk.既然是一個晴朗的天,我們不妨步行.
We might as well have gone home as you suggested.我們還不如按你建議的回家去呢.