This is a response to an answer given by Miriam Solomon (http://www.askphilosophers.org/question/3533). In her response Miriam claims that "...in the 16th century, it was against the laws of nature to claim that Earth moves around the sun." Surely this is missing the point. It was not against the laws of nature but against the contemporary "theories" (*approximations* of the laws of nature) in science. Therefore it was not the laws that were wrong (as she claims), but the theories. Furthermore, to develop upon the original question; the existence of ghosts contradicts currently-held theories of science but also the very conception of ghosts is *self-contradictory*. (For example; If ghosts are capable of physically interacting with their environment they are subject to the action-reaction law of classical mechanics. But if they are capable of travelling through solid objects they do not exert force upon their environment and are not subject to said law: a contradiction.) From this perspective isn't asking "what evidence do we have for the existence of ghosts"? the same as asking ("what evidence do we have for the existence of square-circles"?)?