A treatise called The Art of So and So was a body of general rules, explanations, examples, warnings and recommendations, the study of which was calculated to help the student to become proficient in the practice in question. It was a training manual. Protagoras is said to have written an Art of Wrestling. Some people may learn to wrestle well from mere flair, habituation and imitation; but there is much to be learned also from the technical theory of wrestling. The same thing is true of medicine and navigation. Rule of thumb is not enough.