  In contrast, while Broadbent (2009, 2015), Williams (2011), and Khalidi (2013) agree that diseases lack essential properties, they claim that disease classifications in light of distinctive causes, or types of cause, either pick out distinctive “deviations from normal functional ability,” or (in Khalidi's case) homeostatic property cluster kinds. For instance, Broadbent’s (2009, 2015) “contrastive” model of disease classification roughly takes diseases to be distinct in light of distinctive causes. Where there is a difference in at least one of a set of causes shared by “controls” and “cases” (where cases are identified in light of “parts and processes deviating (negatively) from normal functional ability”), we have a distinct disease. Broadbent takes this account to explain why, for instance, “cervical cancer is a disease, but HPV-itis is not.” Though, it’s not clear that HPV-itis is not properly regarded as a legitimate disease category; or, at least, this case raises an interesting question as to whether potential, rather than overt, dysfunction is more central to disease designation. In public health contexts, whether a strain of HPV causes cancer or not is not as important as deploying interventions that limit the spread of HPV more generally. Strains of HPV that do not currently cause cancer could well evolve the capacity to do so. So, perhaps from a public health perspective, “HPV-itis” is a perfectly legitimate disease category. That is, from a preventive medicine perspective, what matters is that a disease category is a good one for predicting and intervening, even where functional disruption does not always (or even most of the time) eventuate. Which choice of classification we ought to make in demarcating disease types, in other words, might depend on not only on which contrast we are interested in explaining retrospectively, but also which kind of intervention we wish to promote prospectively.