It is however in the process of teaching itself that the spirit of the propagandist may supplant that of the educator. It is much easier to appeal to authority than to experiment, to command assent than to awaken curiosity, to tell the student what he must believe than to wait for the maturing of his judgment. There are five devices commonly in use among propagandists which may defeat the effort for a liberal education. They are the fixation of ideas by repetition, the trick of over-simplification, insinuation by appeal to prejudice, distortion of fact, and coercion. Psychology has taught the advertising profession the selling power of mere monotonous repetition. At one of the stations of the Hudson Tube I counted five posters all displaying the same advertisement of a certain shaving cream. The advertiser had not leased so much space because of extravagance, nor was he afraid that people would fail to notice his advertisement if he displayed it on only one board. It was so large and vivid that the passerby could easily see it. His aim was to deepen the impression by repetition. For the same reason a flashing intermittent electric sign on which the same letters are illuminated again and again is more effective than one with a continuous light. Another example of this method is the poster containing the name of a popular cigarette together with the command, “Read this out loud.” Advertisement of this nature makes no attempt to argue or explain or persuade, or to call attention to the merit of the article for sale. Many commodities in common use owe their popularity not to the fact that people are persuaded that they are superior to a rival but because a trade word has become fixed in memory through endless repetition. A similar method is often used in selling ideas and movements. Santayana says, “A confused competition of propaganda is carried on by the most expert psychological methods--for instance, by always repeating a lie instead of retracting when it is exposed. A formula of this nature may not be a conscious lie, it need only be so fixed in the mind by long repetition that it becomes compulsive. The person who continues repeating it becomes unable to consider the facts which would contradict it.”