Specificity.

Project Gutenberg EPUB3 edition Linebarger, Paul Myron Anthony
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(b) military intelligence which can be released as news;
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(c) military intelligence which cannot be released as news, but knowledge of which will prevent the propaganda operator from making mistakes or miscalculations in reporting the news;
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(e) up-to-the-minute enemy slang, hobbies, fads, grievances, and other matters of current public attention;
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(f) specific grievances of specific groups and of the nation as a whole, should these arise;
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(g) information about probable inter-group conflicts;
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(h) types and forms of discontent with enemy authority;
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(i) identification of unpopular or popular enemy personalities;
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(j) all other information that will enable the psychological warfare operator to act promptly and sympathetically in taking the side of specific enemy individuals against their authorities or other enemy groups.
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Figure 38: Black "Counterpropaganda." Seeing that the Germans had a good counter propaganda medium, the Allies decided to use it themselves. They issued this "counterpropaganda" sheet, shown in original and facsimile in English. The "blackness" is not very black, since few Germans would consider this to be German in origin, once they had read it.
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Enemy opinion cannot be manipulated in general. It must be met on its own ground—the current everyday thoughts of enemy citizens and soldiers. These thoughts do not usually concern grandiose problems of political ethics. They are practical like your own.34 They must be appealed to in a way which makes the listener really listen, makes the reader stop and reread, makes them both think it over later. Getting the attention of the enemy is not enough. Most enemies will pay plenty of attention to you—too much, at times. Getting sympathetic attention is what counts.
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This can be done only with specific grounds. With the news, you and he have a genuine common interest. Using his real troubles as a link, you must create that common interest. The force, the effectiveness of your argument may make him forget that it is the enemy who has brought his attention to this issue. You must leave him with the feeling, "By golly, that fellow is right!"
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But to talk about his troubles, effectively, you must know what they really are. You must see it his way before you start showing him that his way is your way, that you think that he is really on your side, and that his bosses' side is wrong, incorrect and doomed to get whipped, anyhow. Propaganda can operate only on the basis of specificity. Real persuasion can be sought only on the basis of real sympathy with real troubles. Old, incorrectly guessed, or poorly described issues are worse than none at all.

Source attribution

Psychological Warfare, Project Gutenberg eBook #48612

Interrogation. CHAPTER 9 Estimate of the Situation