Toulmin's first, most enduring contribution to keeping philosophy sensible came in his 1958 book, The Uses of Argument (Cambridge University Press). Deceptively formalistic on its surface because it posited a general model of argument, Toulmin's view, in fact, was better described as taxonomic, yet flexible. He believed that formal systems of logic misrepresent the complex way that humans reason in most fields requiring what philosophers call "practical reason," and he offered, accordingly, a theory of knowledge as warranted belief.