Theories are attempts at an accurate description of some part of the world. Models are metaphors, analogies that explain the parts we don’t understand in terms of the parts we do. Models tell you what something is more or less like; theories try to tell you what something is. Models stand on someone else's feet. Theories stand on their own. Financial models are not theories; they are analogies, idealizations that always sweep dirt under the rug. Good models and good modelers have an obligation to make the the dirt explicit.