Might: to express possibility "I might be able to run fast" Could:used to indicate ability or permission in the past. " I could run just as fast" " I could go to work but I won't"

If you "could "do something, then you are perfectly capable of doing it, you just need to decide if you want to. If you "might" do something, means that perhaps you may go ahead and do it. Example: You could go on a trip to Disneyland if you have the money and the capability to get there, all that is needed is to decide if you want to You might go on a trip to Disneyland: you might go if you have enough money and a way to get there, but you are still trying to figure out if it is possible.