2015 Mad, but Not a Madman Insanity — a very specific quality is generally associated with this word. Insanity is viewed as an illness that affects certain people. This illness is permanent and in some way prevents a person from behaving or thinking reasonably or of his or her own accord. Although the most popular, this definition of insanity is not the only one. There are people who other views of what insanity is. Mary Shelley was one such person. In Frankenstein, she demonstrates this opinion