 This section discusses what it takes for these models to be accurate—what the world must be like to host the relations of influence described by the model. However, it must be noted that not every author in the literature would be happy with the way this question is posed. Many prefer to talk about whether a model is appropriate or apt. This is in part because they recognize that many of the models written down and used in practice misrepresent the world. For instance, the models portray systems as deterministic, neglecting minute quantum mechanical chances. Thus, Halpern writes that