 Two conceptual shifts that have marked contemporary research in immunology have influenced philosophical comment on various topics in biology. The first is a major revision in how the mechanics of immunity are conceived. Taking account of the context in which the immune reaction is regulated, the earlier conception of immune specificity as arising from some simple mechanical lock and key matching between selected antibodies binding to noxious antigens has been replaced with collectivist models of molecular interactions. In accounting for the frequency and intensity of an immune encounter, this dynamic orientation portrays the immune system as a sensor of change rather than structure. The sensitivity of such a cognitive system that must mediate multifarious immune reactions requires a co-ordination of collective molecular ensembles, in which diverse elements together determine the extent of the immune response (Daëron 2014). Indeed, only through modulated responses can immunity fulfill its diverse functions, some of which require tolerance of recognized substances and others full blown activation of rejection. Accordingly, immune theory has departed from the classical, self/nonself framework that depicts the immune response as a simple “on” and “off” binary switch, to multifaceted models that account for a spectrum of reactivities.