John Thelwall's diverse achievements in the fields of literature, science and politics have been read as the reason for his omission from the Romantic literary canon. But Thelwall’s scientific research arms him with a unique understanding of the connections between these disciplines, which upset the very notion of canonicity. Thelwall’s model of sympathy, developed in his Essay Towards a Definition of Animal Vitality (1791) offers a physiological understanding of the term which he applies to radical effect in his literary and political works. For Thelwall, sympathy is the physical force through which one organ of the body is inextricably connected with the rest. This physical model radicalises the sentimental tropes Thelwall employs in The Peripatetic (1793), where benevolence is figured as an instinctive impulse. In Thelwall’s political lectures, sympathy is an index of solidarity, but its rational, material basis offers a riposte to charges that Thelwall seeks to exploit the unruly energies of his audience. Thelwall figures sympathy instead as the medium for his political ideal, the diffusion of information and ideas.