Aristotle, Rhetoric
J. H. Freese, Ed.

Now, that which is persuasive is persuasive in reference to some one, and is persuasive and convincing either at once and in and by itself, or because it appears to be proved by propositions that are convincing²; further, no art has the particular in view, medicine for instance what is good for Socrates or Callias, but what is good for this or that class of persons （for this is a matter that comes within the province of an art, whereas the particular is infinite and cannot be the subject of a true science）; similarly, therefore, Rhetoric will not consider what seems probable in each individual case, for instance to Socrates or Hippias, but that which seems probable to this or that class of persons. It is the same with Dialectic, which does not draw conclusions from any random premises—for even madmen have some fancies—but it takes its material from subjects which demand reasoned discussion, as Rhetoric does from those which are common subjects of deliberation.