“The demagogue is one who preaches doctrines he knows to be untrue to men he knows to be idiots.”
Part 2, chapter 4 http://books.google.com/books?id=Xw-DAAAAMAAJ&q=%22The+demagogue+is+one+who+preaches+doctrines+he+knows+to+be+untrue+to+men+he+knows+to+be+idiots%22&pg=PA103#v=onepage
1920s, Notes on Democracy (1926)
Context: The demagogue is one who preaches doctrines he knows to be untrue to men he knows to be idiots. The demaslave is one who listens to what these idiots have to say and pretends to believe it himself.
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H.L. Mencken 281
American journalist and writer 1880–1956Related quotes

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Jesus, The Son of Man (1928)
Context: There are the men who say, "He preached tenderness and kindliness and filial love, yet He would not heed His mother and His brothers when they sought Him in the streets of Jerusalem."
They do not know that His mother and brothers in their loving fear would have had Him return to the bench of the carpenter, whereas He was opening our eyes to the dawn of a new day.
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“Men, forgive Him, for He knows not what He has done.”
Source: The Gospel According to Jesus Christ (1991), p. 347; Jesus' last words from the cross.
Context: Jesus then realized he had been brought here under false pretences, as the lamb is led to sacrifice and that his life had been planned for death since the very beginning. Remembering the river of blood and suffering that would flow from his side and flood the entire earth, he called out to the open sky where God could be seen smiling, Men, forgive Him, for He knows not what He has done.