As a branch of medicine, psychiatry is committed to the medical paradigm which assumes that there are such things as mental illnesses. In this chapter I will define the medical paradigm, identify its virtues, and highlight the areas where it comes under fire —it will be with these challenges and the defence of the medical paradigm that the rest of the book is concerned. As will become clear, both the medical paradigm and its challengers make philosophical assumptions, and only when we identify and clarify these will we solve the difficulties generated. Thereby, a philosophic foundation for psychiatry will be provided.