This article examines the isomorphic connections between the scientific and political ideas of William Lovett and the National Association for the Political and Social Improvement of the People. It demonstrates that, far from being a mere coincidental device, distinct from his politics, Lovett's scientific ideas helped shape the internal structure of his political radicalism. The same was also true of the National Association more generally. Concepts and assumptions derived from phrenology and physiology served the heuristic function of stimulating the construction of analogous systems which directed and conditioned the version of political radicalism which Lovett and the National Association propagated. This suggests that in the mid-nineteenth century the importance of the organic sciences was more politically subtle than previously thought and that a reconciliation of the ideas of George Combe with political radicalism was possible. This insight is compatible with recent historiographical trends, and opens up new vistas for the study of science in radicalism.