 Campbell was a leading member of the school of common sense philosophy. For him common sense is an original source of knowledge common to humankind, by which we are assured of a number of truths that cannot be evinced by reason and “it is equally impossible, without a full conviction of them, to advance a single step in the acquisition of knowledge” (Philosophy of Rhetoric, vol. 1, p. 114). His account is much in line with that of his colleague James Beattie: “that power of the mind which perceives truth, or commands belief, not by progressive argumentation, but by an instantaneous, instinctive, and irresistible impulse; derived neither from education nor from habit, but from nature; acting independently on our will, whenever its object is presented, according to an established law, and therefore properly called Sense; and acting in a similar manner upon all, or at least upon a great majority of mankind, and therefore properly called Common Sense” (An Essay on the Nature and Immutability of Truth, p. 40). We are plainly in the same territory as Reid’s account: “there are principles common to [philosophers and the vulgar], which need no proof, and which do not admit of direct proof”, and these common principles “are the foundation of all reasoning and science” (Reid [EIP]).