In the widespread affective turn, with all its diverse claims for distributed cognition, embodiment, emergence, emotion, feeling, connectedness and shared animality or companionship with non-humans, there would seem to be one point of consensus: we are not Cartesian. We are not minds contingently or unfortunately housed in bodies; we are not brains in a vat, or ghosts in a body that is nothing more than a machine. If there is any ‘we’ or unity today it is perhaps defined by one point of consensus; there is no such thing as mind that is not an emergent property of a broader milieu of affect. In this chapter I want to make three claims. This broad consensus derives from Heidegger’s criticism of Descartes, and his argument that logic and subjectivity are effects of a comportment to the world. Second, what has not been so well discussed is that Heidegger’s criticism of Descartes nevertheless argues that there is a certain Cartesian comportment, or mood. Finally, it is the sense of loss of this Cartesian comportment – the fragility of Cartesian feeling – that typifies many twenty-first-century expressions of preliminary post-human mourning.