This is the first complete English translation of On the Purity of the Art of Logic, a handbook of logic written in Latin by English philosopher Walter Burley (c.1275-1344/5). The work circulated in the Middle Ages in two versions, a shorter and a longer one, both translated here by Paul Vincent Spade. The translations are based on the only complete edition of Burley's treatises, corrected by Spade on the basis of one of the surviving manuscripts...