In 2020, M. Summa developed a promising approach to understanding the concept of illness. This approach combines a theory of organisms with Responsive Phenomenology to gain a concept of illness. Following on from this, the present article shows that the normative presuppositions can be further explicated and justified by drawing on the theoretical resources of Aristotelian naturalism as propounded by Michael Thompson. Aristotelian naturalism does provide a theoretical option to grasp the normative foundations of human life. However, this article argues (...) that Aristotelian naturalism requires another criterion besides human nature to make the concept of illness intelligible. Following John McDowell’s critique of Aristotelian naturalism, it will be shown that this criterion consists in the capacity for autonomy. From this a concept of illness is developed which describes an impairment of the self-regulated and autonomous realisation of the human form of life. (shrink)