In the aftermath of the great bailout of capital in 2008 (and still ongoing) finance has often been seen as external and parasitical to the real economy. Instead, finance and other forms of capital have become more closely articulated and interwoven. A critical social logic of the derivative is offered here, following on Marx’s analysis of the commodity, to consider what is meant by dominance of finance, what difference finance makes and the politics of debt. The derivative provides key insights into the apparently detached process by which money seems to beget more money, and at the same time discloses the internal socialization and interdependence that is at the root of a politically generative mutual indebtedness.