To be published in Pierre-Olivier Méthot (dir.), Health, Medicine, and Society: Essays on the Philosophy of Georges Canguilhem, Hermann 1 The Individual Relativity of Health and Disease: Personalized Medicine in the Light of Canguilhem’s Philosophy of Medicine Elodie Giroux, elodie.giroux@univ-lyon3.fr Université Jean Moulin Lyon 3, Institut de Recherches Philosophiques de Lyon (IRPhiL, EA 4187) Abstract The progress of so-called “personalized medicine”, in particular in the context of the development of targeted therapies in oncology, leads to more precise definitions, diagnostics and treatments of diseases. This could give rise to the constitution of ever smaller classes of diseases. Further, via an approach that aims to be both dynamic and holistic, “systems medicine” and in particular “P4 medicine” (preventive, predictive, participative, and personalized) advocates an individualization based on observation of the transition between health and disease for each individual, thanks to repeated monitoring of various genomic, clinical, psychical, environmental, and social characteristics. These different forms of individualization echo the theses of Canguihem, according to which there is no general definition of the normal and the healthy but only a universal biological normativity, which, in each biological individual, takes an individual form. That idea led Canguilhem to affirm the impossibility both of a science of the normal and the pathological and of complete objectivity with regard to these phenomena. Systems medicine, by contrast, and in particular P4 medicine, promotes both a quantification and a science of well-being. The aim of this chapter is to examine the forms of individualization of health and disease which give rise to the two principal orientations of personalized medicine – the stratified medicine, the precision medicine, already used in oncology, and the more theoretical systems medicine – and then to confront them with Canguilhem’s thesis regarding health and disease. In this way, I will develop a critical analysis of the promises and pretentions of personalized medicine, and in particular P4 medicine. What today goes by the name of “personalized medicine” covers a diverse range of subsidiary projects and a concomitant multiplication of more precise labels: genomic medicine, molecular medicine, stratified medicine, P4 medicine (preventive, predictive, participative, and personalized), network medicine, precision medicine, patient-centered medicine, medicine of the person, and so on. Most of the projects do, however, share the common trait of centering attention on the individual, on inter-individual variability, and on the development of treatments based on knowledge of individual characteristics. According to “precision medicine” or “P4 medicine”, more precise and detailed knowledge of health phenomena, made possible by the collection – for a single individual – of a great amount of data, could lead to more effectively individualized treatment and care. Our current disease classifications could thereby evolve, and perhaps even disappear, as each disease is precisely described as a function of the particularities of each individual. It is often underlined that one no longer seeks to treat the disease, but the ill person. In particular, the objective of P4 medicine, on which my analysis will concentrate, is to collect a great number of longitudinal