The meaning of King's monumental quote is more complex today than in 1963 because "the unconscious signals have changed," says the historian Taylor Branch, author of the acclaimed trilogy "America in the King Years."
Fifty years ago, bigotry was widely accepted. Today, Branch says, even though prejudice is widely denounced, many people unconsciously pre-judge others.
"Unfortunately race in American history has been one area in which Americans kid themselves and pretend to be fair-minded when they really are not," says Branch, whose new book is "The King Years: Historic Moments in the Civil Rights Movement."
Branch believes that today, King would ask people of all backgrounds — not just whites — to deepen their patriotism by leaving their comfort zones, reaching across barriers and learning about different people.
"To remember that we all have to stretch ourselves to build the ties that bind a democracy, which really is the source of our strength," Branch says.
Bernice King says her father is asking us "to get to a place — we're obviously not there — but to get to a place where the first thing that we utilize as a measurement is not someone's external designation, but it really is trying to look beyond that into the substance of a person in making certain decisions, to rid ourselves of those kinds of prejudices and biases that we often bring to decisions that we make."
That takes a lot of "psychological work," she says, adding, "He's really challenging us."
For many conservatives, the modern meaning of King's quote is clear: Special consideration for one racial or ethnic group is a violation of the dream.
The quote is like the Declaration of Independence, says Roger Clegg, president of the Center for Equal Opportunity, a conservative think tank that studies race and ethnicity. In years past, he says, America may have needed to grow into the words, but today they must be obeyed to the letter.