George Campbell was part of the epistemological tradition, as would be Whately. Faculty psychology tried to explain behavior in terms of five powers of the mind--understanding, memory, imagination, passion, and will. Campbell defined rhetoric in terms of these same five faculties. Campbell's theory was that rhetoric must address all the faculties of the mind to achieve persuasion, and he set forth a detailed theory of the faculties, their purposes, and the forms appropriate for appealing to each, stating that the path to persuasion passes through each of the faculties in turn. Professor Dominic LaRusso argues that Campbell's The Philosophy of Rhetoric is not "revolutionary, unique, and important," countering the claim to the contrary by Professor Douglas Ehninger. LaRusso may be correct that the work is not revolutionary or unique, with the first being in part a value judgment and the second an assessment based on a comparison of the work to what went before. The work is clearly important, however, for it disseminated a variety of ideas to others and had a demonstrable influence on subsequent theorists such as Whately, an influence that might not have occurred had the book not been written even if it only codified earlier ideas.
George Campbell was one of the proponents of the Scottish philosophy of common sense that would be so important in maintaining the old tradition of rhetoric in Great Britain:
This tradition, in which the theory of invention is reduced to a minimum and interest is focused on the persuasive aspect of discourse, is represented by such original works as George Campbell's The Philosophy of Rhetoric (1776) and Richard Whately's Elements of Rhetoric (1828).
Campbell based his rhetorical theory on the psychology of John Locke while taking into account the contemporary concerns of rhetoric for elocution, grammar, pulpit oratory, literary criticism, and the abiding connection of rhetoric with its classical...