This paper identifies two broad strands of fiscal theorizing which date back to the late 19th century in the persons of Knut Wicksell (1896) and Francis Edgeworth (1897). From Edgeworth descends the treatment of public finance as a branch of applied statecraft, as conveyed these days largely through notions of optimal taxation. From Wicksell descends the treatment of public finance as offering explanations for observed patterns of collective activity. These two branches are not so much antagonistic as they are non-commensurable. The explanatory branch, moreover, is underdeveloped in comparison with the hortatory branch, and this paper seeks to sketch some contours for an explanatory theory of collective activity, paying particular attention to the American fiscal context.