The principles of definition, the law of
contradiction, the fallacy of arguing in a circle, the distinction
between the essence and accidents of a thing or notion, between means
and ends, between causes and conditions; also the division of the mind
into the rational, concupiscent, and irascible elements, or of pleasures
and desires into necessary and unnecessary—these and other great
forms of thought are all of them to be found in the Republic, and were
probably first invented by Plato.