"Many people know Hadot outside of France for his influence on Foucault’s later work. Foucault’s work on the history of sexuality was largely indebted to Hadot. In Hadot as in Foucault, there’s the preoccupation with philosophy as epimeleia heautou (care of the self), and as being principally concerned with the cultivation of happiness, where the theoretical concerns are secondary in some cases. As in the Stoics, you need to have a correct view of, say, physics—of how the natural world works—in order to be happy, because if you don’t, then you’ll constantly be slipping up in your interpretation of what’s going on in the world, which will make you unhappy.
Now, I’ve actually been interested in making a case that something similar continues well into the 17th century. Descartes and Leibniz both continue to share such a conception of the project of philosophy, which is why they’re both so preoccupied with things like pharmaceutical recipes and studying problems having to do with health and illness, because it’s central to the cultivation of ‘the good life’. Hadot stops in Late Antiquity, in Hellenistic philosophy. Foucault follows him in that regard. My suspicion is that it’s actually a very long and continuous tradition. This is yet another sense in which the early moderns are more continuous with the ancients than we often think they are. The real break is not in the 17th century, but in the 19th century."