Was ‘I have a dream’ improvised? King’s own account of his 1963 Washington speech says yes
The refrain was not in the text King prepared for August 28, 1963, but he had used it in Rocky Mount in 1962 and in Detroit two months before the march.
Martin Luther King Jr.
King’s ‘arc of the moral universe’ line adapts an 1853 sermon by abolitionist minister Theodore Parker
Theodore Parker's 1853 sermon used 53 words and admitted doubt; King's 13-word version, used from 1958 and in Montgomery in 1965, turned it into a promise.