In our era of pre-washed soundbites and speeches which have been pre-tested on focus groups before being stripped bare of ideology or radicalism, it's sometimes difficult to imagine that there was a time when there were passionate public speakers who could change a climate or set a public mood.
Speakers who could stand before thousands, maybe tens of thousands of people, and row them in behind a cause and persuade them to be bolder than they could ever have believed themselves to be.
Inspire them to believe that change was possible, irrespective of the odds stacked against them.
Martin Luther King was such a speaker. An African-American Baptist minister, he had been involved in the civil rights campaign since the early 1950s and had risen to national prominence as the leader of a campaign to desegregate public buses in Montgomery, Alabama, in 1955-6.
But he is best remembered for a speech he delivered in Washington on August 28, 1963, in front of 200,000. It's still referred to as the 'I have a dream' speech, even though the words were not included in his prepared text.
The speech was the high point of the March on Washington for Jobs and Freedom: and the march itself was the focal point of a campaign against discrimination, voting restrictions, unfair treatment by the police and statutory barriers against social mobility and economic opportunity.
Oddly enough, King wasn't actually the main speaker of the day: but the power of his language and the clarity of his passion ensured that his was the speech that is still remembered.
It was a speech seen around America and around the world. It came a few months after the world's media had captured footage of police beating crowds of peaceful protesters in Birmingham, Alabama, and was seen by many, including many white liberals in America's political establishment as a powerful, peaceful, unanswerable case for justice: "a promissory note that all men – yes black men as well as white men – would be guaranteed the unalienable rights of life, liberty and the pursuit of happiness".
In other words, the demonstrators were asking for nothing more than the rights supposedly guaranteed to all Americans in the country's founding documents, declarations and constitution.
Within two years of that speech, both the Civil Rights Act of 1964 and the 1965 Voting Rights Act had been passed. America and American public opinion was changed by that speech. The change is not yet complete but, as an editorial in The Economist noted: 'America's shameful past is fading. Skin colour is nothing like the barrier it once was. But the pursuit of happiness to which King referred is never easy, and never ends.'
Back in Northern Ireland, a new generation of young, educated, articulate nationalists was beginning to emerge. They saw the footage of events in Birmingham, Alabama. They saw the grainy footage of King's address in the shadow of the Lincoln Memorial. They saw what was possible when ordinary people gathered together and sang 'We shall overcome'.
More important (and remember that King's speech came a few months after the IRA ended their 1956-62 border campaign) those young nationalists looked at the language of American Civil Rights and the target of the campaign.
It wasn't about coloured people asking for a separate state and their own rights: rather, it was about American citizens asking for precisely the same rights as every other American citizen.
And King's demand for an end to discrimination, equality of voting and jobs and the right not to be viewed and treated as lesser, second-class citizens was the language adopted by the Civil Rights campaign in Northern Ireland. The marches, demonstrations and tactics were also adopted and adapted.
So, when someone asks if a speech – one particular speech – can change history, then the answer is yes; yes it can. It can change it in the place it was made and the ripples of that speech can spread across the world.
When President Reagan stood in Berlin and said (in a message intended for Russian president Gorbachev), "Mr President, tear down this wall", it was the culmination of a very powerful speech that changed the nature of European and world politics. It captured the moment. It gave key people on both sides of the Berlin Wall the courage and incentive to change.
It can work on a more personal level too. Just before his men were due to go to Iraq in March 2003, Belfast-born Colonel Tim Collins told them: "It is a big step to take another human life. It is not to be done lightly. I know of men who have taken life needlessly in other conflicts. I can assure you that they live with the mark of Cain upon them. You will be shunned unless your conduct is of the highest, for your deeds will follow you down through history. We will bring shame on neither our uniforms nor our nation."
No gung-ho there. No false heroics or jingoistic cliche. Just a very personal, very honest, very emotional speech. A speech that went around the world. It made an impression because those who heard it knew he meant every word of it: and that's always the bedrock of every speech that is remembered down the years.