The passage below is chapter vi of George Campbell's book The
Philosophy of Rhetoric, published in 1776, where he argues
against the utility of the 'school logic', i.e. traditional or
Aristotelian logic. It illustrates well the low point to which
logic had fallen in the eighteenth century. (For more
eighteenth-century musings about logic, see Reid's commentary on
Aristotle's Organon). He repeats a point made by Locke, that
'the syllogistic art, with its figures and moods, serves more to
display the ingenuity of the inventor, and to exercise the
address and fluency of the learner, than to assist the diligent
inquirer in his researches after truth'. Campbell argues that
syllogistic demonstration involves a petitio principii, i.e. it
assumes as a premiss, the very thing it was to prove. For
example: All animals feel; All horses are animals; Therefore all
horses feel. A sceptic will object that the premisses are merely
an affirmation of the point which he denies, i.e. all animals
feel, is only a 'compendious expr