Though widely associated with Bob Marley and his incredibly popular “Redemption Song” lyric, the phrase “emancipate yourselves from mental slavery” is a paraphrase from a speech by Marcus Garvey. In his comments during a speech entitled “The Work That Has Been Done” in November 1937 he said:
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“We are going to emancipate ourselves from mental slavery, because whilst others might free the body, none but ourselves can free the mind. Mind is our only ruler; sovereign.”
More of the fascinating mind of Marcus Garvey can be found in the book Emancipated from Mental Slavery: Selected Sayings of Marcus Garvey.