Eighteenth century Scottish philosopher Thomas Reid's emphasis on first principles of knowledge is fundamental to his ethics of rhetoric. Reid found the reduction of mental activities to material phenomena by Hobbes and others to be particularly odious and destructive of common sense. Turning to the analysis of human nature, he developed a radical distinction between mental and physical processes and posited the existence of a natural faculty, "common" or "moral" sense, that intuitively perceives truth and falsity. He enumerated sets of first principles governing necessary truths, contingent truths, and moral truths. His six general and five particular first principles of morals apply to three fundamental problems in the ethics of rhetoric: (1) identifying legitimate ends of discourse, (2) legitimizing techniques of influence, and (3) educating the moral rhetor. Although it is unlikely that knowledge of one rhetorical system contributes to knowledge of another, Reid's philosophy has much of potential interest to us because there is a close parallel between the problems he confronted and some with which rhetorical theorists struggle today. (JL)