Every scientific paradigm has its philosophical assumptions; we can hardly find a science that is impartial, unbiased, and neutral. Psychiatry makes no exception. In this chapter, I will first outline some of those philosophical assumptions that concern the nature of mental disorders. I will show that, despite the claim of being a practical discipline, which only aims to cure people, psychiatry starts from a series of postulations, i.e., notions and beliefs that are widely shared but largely unwarranted. I will criticize those assumptions, showing that most psychiatrists are committed to a notion of mental disorder that is flawed (or at least unjustified) and that neglects the very role of the mental. I will then show the importance, in defying mental disorders, of both a mentalist vocabulary and the reference to norms that are cultural, social, moral, and evaluative. At the end of the chapter, I will outline the importance of ethics in psychiatry.