WASHINGTON - It's the most memorable line from one of history's greatest speeches, yet civil rights leader Martin Luther King never planned to say "I have a dream" when he addressed the March on Washington a half-century ago.
King was the last speaker of the day when he took the lectern on August 28, 1963 and looked out over the unprecedented crowd of 250,000 that filled the National Mall for the March on Washington for Jobs and Freedom.
In the hands of the oratorically gifted Baptist preacher from Georgia was a text that he and his associates had painstakingly finalized the night before.
The phrase "I have a dream" was not in it.
"For all King's careful preparation, the part of the speech that went on to enter the history books was added extemporaneously while he was standing on the steps of the Lincoln Memorial, speaking in full flight to the crowd," wrote US-based columnist Gary Younge of Britain's Guardian newspaper in an excerpt of his new book "The Speech."
King had used the "I have a dream" line before, including in a sermon in Detroit recorded by Motown two months earlier. But King's adviser Wyatt Walker counselled against its re-use, contending it was "trite" and "cliche" and basically unworthy of a nationally televised event.
King, introduced to the National Mall rally as "the moral leader of our nation," himself told graduate student Donald Smith later that year that he had "just all of a sudden" decided on the fly to invoke the dream.
He might have been swayed on the spot by Gospel singer Mahalia Jackson, who performed earlier in the day, when she shouted out at him: "Tell 'em about the dream, Martin!"
"I just felt I wanted to use it," King told Smith, who went on to write a Ph.D. dissertation about King's powerful use of persuasive speech. "I don't know why. I hadn't thought about it before that speech."
Sixteen minutes long, the speech became even better known as King's virtual epitaph after he was shot and killed on the balcony of the Lorraine Motel in Memphis, Tennessee in April 1968 by a white sniper across the street.
But it wasn't just what King said that hot summer day in Washington, but who was listening and watching on live radio and television.
"For the first time a mass white audience heard the undeniable justice of black demands," said Julian Bond, then chairman of the National Association for the Advancement of Colored People (NAACP), quoted in Smithsonian magazine in 2003.
King himself remembered the March on Washington as "that radiant August day."