Public opinion is amenable to manipulation, yet it is worthwhile to keep in mind that by teaching the public to obtain the desired, the “manipulator” defends it against its own aggressiveness. In the study of the public opinion at large, the methods of experimental psychology do not prove to be as efficient as the methods of introspective psychology. To be able to form, and to alter public opinion, it is necessary to comprehend people’s motives, to be aware of the interests they have at the moment, and to understand very well the functions – as well as to perceive the scantiness of the physical means of access to the public – of such facilities as radio, tribunes, cinema, letters, newspapers and so on.