Adorno rightly thought of Negative Dialektik as his major work of philosophy. The book that he dubbed his “fat child” is notoriously difficult, and as problematic as it is intriguing. In this article I lay out two of its central problematics. The first concerns Negative Dialectics as (and against) metaphysics; the second pertains its tacit ethical or moral dimension. I shall set out these two problematics in such a way that each illuminates the other. It will also allow me some reflections on Adorno’s conflicted stance towards humanism: on the sense in which endorses humanism, and the sense in which he rejects it. I shall argue that Adorno’s humanism contains a moral notion of solidarity that plays a pivotal role in Negative Dialectics. Together, the idea of the human, and the notion of solidarity it contains, can when suitably interpreted, explicate and justify what Michael Theunissen calls Adorno’s positive premise in Negative Dialectics, and can do so in a way that is broadly consistent with his negativism.