On Tyranny uses the darkest moments in twentieth-century history, from Nazism to Communism, to teach twenty lessons on resisting modern-day authoritarianism. Among the twenty include a warning to be aware of how symbols used today could affect tomorrow (“4: Take responsibility for the face of the world”), an urgent reminder to research everything for yourself and to the fullest extent (“11: Investigate”), a point to use personalized and individualized speech rather than clichéd phrases for the sake of mass appeal (“9: Be kind to our language”), and more.