Proust wrote vividly about grief, but he has not been recognised or studied as a philosopher of grief. It is time that he was. For a powerful and compelling philosophy of grief emerges from the pages of his magnum opus. Though philosophical work on Proust has not turned to this theory of grief, philosophers writing about grief have often drawn on Proust, both explicitly and implicitly, without an awareness of an underlying Proustian theory. This paper fills the gap by placing (...) this philosophically informed, Proustian theory of grief before our eyes. Proust builds on contemporary discussions of habituation (habitude), the process whereby new sensations and new actions become both less salient, intrusive or demanding of our attention, and more crucial for our equilibrium and our continued short-term functioning. Applying this to the social realm, Proust theorises love in terms of habituation to another person, and grief in terms of a sudden inapplicability or unsuitability of our habits to the world that person has left behind, followed by the painful, uneven and intermittent process of habituating to that new world. The paper explains this theory and charts its relation to some contemporary discussions of grief. Doing so places Proust back into a conversation he has already influenced. (shrink)