In the conclusion to this multi-part article I first review the discussions carried out around the six essential questions in psychiatric diagnosis - the position taken by Allen Frances on each question, the commentaries on the respective question along with Frances' responses to the commentaries, and my own view of the multiple discussions. In this review I emphasize that the core question is the first - what is the nature of psychiatric illness - and that in some manner all further questions follow from the first. Following this review I attempt to move the discussion forward, addressing the first question from the perspectives of natural kind analysis and complexity analysis. This reflection leads toward a view of psychiatric disorders - and future nosologies - as far more complex and uncertain than we have imagined.