Norman Geras argues for the incorporation of elements from the just war tradition into the ethics of social change. But this does not go far enough. In this paper I argue for a prefigurative constraint: that action intended to bring about social transformation ought to prefigure that transformation, and bear those properties of the future state of affairs that make the future state of affairs morally valuable. I defend the idea of a prefigurative constraint against some objections and introduce a schema to relate political action to morally valuable end states