Cohen draws attention to the advantages of being a child psychiatric investigator: not only is he present at the beginning of individual development, but his background and experience enable him to assess data correlating body, mind, and environment. Furthermore, his comprehensive medicopsychological education gives him the freedom to range from genetics to sociology, taking in psychology, psychoanalysis, child development, and pediatrics on the way. However, he points out that this “linguistic versatility” has some dangers attached to it in that there is a certain risk of becoming a somewhat confused polyglot. The chapter is remarkable in several different ways. It displays a scholarship and a philosophical understanding of epistemological issues that is well beyond the knowledge of the average clinical investigator, who is unlikely to have read Descartes, let alone to have written a thesis on him. In such hands, the analysis of models becomes a highly sophisticated exercise, which could be of little more than academic interest were it not for the important fact that it is made operational through a study of eczematous children. To use a model deriving from Wittgenstein is an extraordinary thing and puts to shame those of us still grappling with hydrostatic structures designed for a simpler age.