When Coleridge began dictating his Biographia Literaria in 1815, he was at the same time becoming actively involved in a medico-philosophical controversy that was then drawing the attention of many medical men and philosophers in England. The fundamental issue behind the quarrel, a materialistic versus a vitalist theory of nature, was one Coleridge had argued in one form or another throughout his career.1 Yet, the challenge of modern science specifically had never been so strong nor had it so vociferously demanded his attention as it did in the years from 1814 to 1819. Coleridge's response is well documented: the revised and enlarged version of The Friend, his Lay Sermons, the "Theory of Life," and a series of philosophical letters written between November 1816 and January 1818 all testify to Coleridge's growing concern with the challenge of science to his philosophy and to his need to validate his philosophical beliefs with scientific evidence.