can是表示请求、给予或拒绝许可的最通用词
Can I borrow your pen?
may用以表示礼貌的正式请求或给予许可
You may come if you wish.
might是may的过去式,用于间接引语
He said he might come tomorrow.
must用于现在时,表某事有必要或应该做.
I must wash the car tomorrow.
还用以表示说话者或听话者的主观意愿
I’d love to stay,but I must go now.
probably 意思是几乎肯定、很可能、大概
You're probably right.