That a Syllogistic or Logic of Consistency should emerge out of Yes-and-No Dialectic was natural. Things in this world come when they are wanted: inventions are made on the spur of necessity. It was above all necessary in this kind of debate to avoid contradicting yourself: to maintain your consistency. A clever interrogator spread out proposition after proposition before you and invited your assent, choosing forms of words likely to catch your prejudices and lure you into self-contradiction. An organon, instrument, or discipline calculated to protect you as Respondent and guide you as Questioner by making clear what an admission led to, was urgently called for, and when the game had been in high fashion for more than a century Aristotle's genius devised what was wanted, meeting at the same time, no doubt, collateral needs that had arisen from the application of Dialectic to various kinds of subject-matter. The thoroughness of Aristotle's system was doubtless due partly to the searching character of the dialectic in which it had its birth. No other mode of disputation makes such demands upon the disputant's intellectual agility and precision, or is so well adapted to lay bare the skeleton of an argument. The uses of Aristotle's logical treatises remained when the fashion that had called them forth had passed.[6] Clear and consistent thinking, a mastery of the perplexities and ambiguities of language, power to detect identity of meaning under difference of expression, a ready apprehension of all that a proposition implies, all that may be educed or deduced from it--whatever helps to these ends must be of perpetual use. "To purge the understanding of those errors which lie in the confusion and perplexities of an inconsequent thinking," is a modern description of the main scope of Logic.[7] It is a good description of the branch of Logic that keeps closest to the Aristotelian tradition.