Campbell embraced the philosophical empiricism which John Locke established in An Essay Concerning Human Understanding. Following the example of Locke's humanistic sciences, Campbell set forth an analysis of rhetoric through the scope of mental faculties. He believed that a rhetoric grounded in empiricism would become efficient because of the incorporation of the cognitive processes. The human senses are the basis for the validity of belief; thus a rhetorical theory based in faculty psychology would establish that rhetoric is capable of making a reader experience a concept with the same "vivacity" and automaticity as that of the senses.