i'm a chinese.about the question of you。可是 and 却 are very similar in the meaning。but，there is some difference in the emotion of them。
such as
我认为这是对的，可是你不这么认为
我认为这是对的，你却不这么认为
我认为这是对的，可是你却不这么认为
the emotion of stress about “你（you）”，become more and more heavy。