US President-elect Barack Obama's rhetorical skill, his ability to captivate and inspire audiences with his powerful speeches, has led some writers to describe him as the greatest orator of his generation.

The power of the word: Mr Obama is inspired by earlier orators

What is the secret of his success - the words themselves, the way he delivers them, or the historical change he represents?

"I believe Barack Obama embodies, more than any other politician, the ideals of American eloquence," says Ekaterina Haskins, professor of rhetoric at the University of Iowa.

His speeches, she argues, are shaded with subtle echoes of great speeches past, consciously creating a sense of history, purpose and continuity.

Past ghosts

"He has certainly studied all of his predecessors, he is quite aware of the rhetorical heritage that he draws on," Ms Haskins explains. "He clearly sees himself as a descendant of Abraham Lincoln and Martin Luther King."

"He is summoning the ghosts of previous leaders and presidents who Americans have learnt to revere."

ECHOES OF THE PAST MARTIN LUTHER KING: I may not get there with you but I want you to know tonight that we as a people will get to the promised land BARACK OBAMA: The road ahead will be long. Our climb will be steep. We may not get there in one year or even one term. But, America, I have never been more hopeful than I am tonight that we will get there. I promise you, we as a people will get there

On winning the election, his Chicago address echoed two of the most famous speeches in US history - Abraham Lincoln's 1863 Gettysburg address and the words spoken by assassinated civil rights campaigner Martin Luther King the day before his death.

Philip Collins, a speech-writer for former UK Prime Minister Tony Blair, is in no doubt that Mr Obama owes his success to his oratorical gifts.

"He has shown the power of brilliant rhetorical force," says Mr Collins, a leader writer for the UK's Times newspaper.

Initially, Mr Obama's speeches, peppered with references to lofty ideals like "change", "promise" and "belief" prompted criticism that they were devoid of content and policy.

He began to add policy detail as the campaign progressed but his speech at the Democratic Convention was regarded as less engaging by some observers, precisely because of the amount of concrete proposals it contained.

Peopled by personalities

Ms Haskins argues that Mr Obama has other techniques for avoiding the charge of pure rhetoric, adding weight and depth to the abstract with solid illustrations.

"Rhetoric always has the connotations of being about appearances rather than reality but he doesn't sound false. He plays with the patriotic abstractions that allow for a certain kind of rhetorical manoeuvring and fills them with specific concrete examples," she says.

His victory speech, delivered in Chicago, channelled broad ideas of the struggle of a generation through the eyes of 106-year-old Ann Nixon Cooper, who has become a celebrity in her own right.

But does the poetry of his campaign risk stumbling when it faces the more prosaic role of holding office?

RACE SPEECH IN FULL Barack Obama: A More Perfect Union [55KB] Most computers will open this document automatically, but you may need Adobe Reader Download the reader here

Many commentators pinpoint the "A More Perfect Union" speech, made in March 2008 in the aftermath of a scandal about his former pastor, Reverend Jeremiah Wright, as one of Mr Obama's finest.

Evidence of Rev Wright's inflammatory sermons risked irrevocably damaging Mr Obama's candidacy but his response managed to tackle the question of race in US society with delicacy.

It was a speech which wrapped the experience of different races together, expressing understanding for the deep-seated, lingering resentments of each and presenting himself as the embodiment of unity.

His style of delivery is basically churchy, it's religious: the way he slides down some words and hits others Philip Collins Journalist and speech-writer

For Mr Collins, it remains the only speech, so far, that will not fade. Rousing campaigning speeches, however perfectly pitched and presented, he says, do not test the true mettle of a politician. What does is a speech that attempts to change the opinions of those who disagree with you.

"The weakness of Obama's rhetoric so far is that it is so agreeable. There is almost nothing he says with which you can disagree. We need to wait for the big moments, the foreign policy challenges, for the great Obama speeches."

'It's about the tune'

Yet print out and read a transcript of a speech by Mr Obama and you may be disappointed. Virginia Sapiro, professor of political science at Boston University, suggests this is because the way Mr Obama delivers his speeches is as important as his words.

"He looks at all times in possession of himself - he is very calm, with an inner peace in his delivery which, in a time of crisis, is very important."

Ms Haskins agrees: "I've been going through his speeches textually. The text alone cannot tell us why they are so powerful, it is about delivery."

He may have calmness, notes Mr Collins, but the range of his delivery - the way he alters his pace, tone and rhythm - is closer to song.

"His style of delivery is basically churchy, it's religious: the way he slides down some words and hits others - the intonation, the emphasis, the pauses and the silences," he explains.

"He is close to singing, just as preaching is close to singing. All writing is a rhythm of kinds and he brings it out, hits the tune. It's about the tune, not the lyrics, with Obama."