Since Aretha Franklin passed away last week, the world has been talking about the phenomenal intensity of her music, her Soul. But why does it move us in this way? War correspondent Ed Vulliamy, who has written a book on the power of music, explains why in times of struggle, conflict or striving for peace, it's the art form we turn to – why we turn to Aretha.

EVEN in the cheapest seats at the back of the upper circle, you could feel the thrill and power. Aretha Franklin – Hurricane Aretha – at Hammersmith Odeon in 1970. Yes, I know, everyone is claiming their nano-corner of this lost legend, but here's mine: the concert came within 24 hours of my 16th birthday and Aretha was all presence and passion; enthralling and electrifying. She was, above all, the sound on her piano, and in her voice: a restive sound like musical touchpaper beyond all words or the ability of words to describe it. Beyond even other comparable music – pop, Motown, even blues or jazz – she was pure Soul, in the essence of the word, and it still rings in my ears. When you heard Hurricane Aretha, you knew something even bigger than her was coming at you down the tracks, of which she was voice and harbinger. And it was.

What was happening that night? A few years earlier, the great singer-songwriter Graham Nash sat behind the Beatles at a concert by Aretha’s compatriot Jimi Hendrix in London, and wondered, he told me, “What on earth is going on?” It’s a very good question – what indeed?

There are times when music – and musicians – say and convey what no other means of communication can. This is a primal truth – we all know it; it’s alchemic, and has obsessed human beings ever since they were able to hear and (to cite the title of my favourite Aretha song) "Think". Ever since Pythagoras posited the idea that music was the sound of celestial spheres.

When President Barack Obama described Aretha Franklin’s voice as "divine" in the wake of her passing on Thursday, he may have been speaking metaphorically – but if he wasn’t, he invoked an old idea: not just that Aretha – like most soul singers – began singing in church, but that of music as expressing the intangible, that which words cannot describe or define. Music as a means of conveying a mystery, an elusive truth, a human emotion, or the story of a people or of a time – present, gone or time to come. Music is a way of speaking something as enigmatic as Soul – which is where Aretha Franklin comes in.

"Words fail", says Samuel Beckett’s character Winnie in his play Happy Days. “There are times when even they fail ... What would I do without them, when words fail." Well, very often, we turn to music, and this weekend many of us have turned to Aretha Franklin.

My upcoming book, When Words Fail, is an attempt to explore why we do this, especially at those times when music intervenes in the world – as a force for peace, against war, for justice – across all time, but my lifetime in particular. War has been my work for much of it, and music my great love since as long as I can remember.

By the time I saw Aretha Franklin, the peace and black civil rights movements were in full bloom in the United States. I was captivated and resolved to save up and go for my first big adventure, to Chicago, which had by then joined the cities of the Deep South and Detroit as a kernel of that war for Afro-American equal and civil rights, and that for peace against war in Vietnam. Music was at the core of, was the driving force for, both, and I went to breathe the hot summer and buy the records that carried whatever it was that words failed to describe. Music was the voice of whatever was happening in America at that time, more than any speech, memoir or manifesto.

It’s fair to say, I think, that the Vietnam War would not have been lost by America without a peace movement at home, like a ball and chain round the military patriots’ ankles, that had music at its core: Joan Baez, Bob Dylan, Jefferson Airplane. And I doubt the civil rights movement ignited by Dr Martin Luther King would have had the impact it did without a song to sing. A song sung by the pantheon that included, among others, B B King and Aretha Franklin.

"Respect!" roared Aretha, adapting Otis Redding. It was couched as a domestic song, about a disrespectful lover, but everyone heard Aretha’s setting to music of everything that had happened since the moment Rosa Parks refused to give up her seat to a white passenger on a segregated bus in Alabama in December 1955. Aretha put that moment, and everything that followed it, to music.

Aretha was, famously, the "Queen of Soul". But Soul is not just a genre of music – it was and is the spirit of a movement, a people, a feeling: Soul Sister, Soul Brother, Soul Food, "Reggae Got Soul", as Bob Marley would later sing. The Oxford English Dictionary defines soul not only as “The spiritual or immaterial part of a human being or animal, regarded as immortal”, but also “Emotional or intellectual energy or intensity, especially as revealed in a work of art or an artistic performance". Aretha was the queen of that, for sure. It also defines it as “Black American culture or ethnic pride”, and she was the queen of that too.

If Martin Luther King was the leader of the civil rights movement, "Soul", in all three definitions, was its engine and beating heart – and the idea of soul found its voice in music. Moreover, after King’s assassination in 1968, Soul changed gear.

On every radio set, at home and in Vietnam, Marvin Gaye's honeyed yearning for love became urgent demands: 'What's Going On' and 'What's Happening, Brother’. The Temptations now spinned a 'Ball of Confusion (That's What the World is Today)', Stevie Wonder saw something different in the mirror of his mind from 'My Cherie Amour' – and was now pleading 'Heaven Help Us All'. James Brown went from 'Papa's Got a Brand New Bag' to 'Say It Loud I'm Black and I'm Proud'.

But Aretha? She was ahead of that curve. She had staked her soul-turf a year before the assassination and three years before I saw her at Hammersmith. She had already recorded Think in 1967: "Think! … Let your mind go, let yourself be free / Oh, freedom". And sung Willie Nelson’s Night Life: “Oh listen to the blues / And what they're are sayin'”. And demanded Respect, and cast off the Chain of Fools. Even before MLK was assassinated and Soul woke up, Aretha was her father’s daughter in every way: CL Franklin was an itinerant preacher of both the Good Book and of black civil rights, and his daughter’s voice had been part of that travelling soulstorm since Aretha was 12 years old.

So Aretha and her songs gave voice to that hinge between the emergent, then explosive, Afro constituency in America that had had enough of wearing those chains, the latter-day shackles of slavery. They'd had enough of segregation, lynching, "No Coloureds", police brutality, white supremacist batons cracking the skulls of Dr King and his marchers, just as they do again today.

Aretha gave a voice to more than people talked about even at the time: to black women specifically – and in another way all women. Hers was a voice that sung of love, accompanied suffering and promised defiance. There was, in that league, Aretha, Nina Simone and Diana Ross. Nina was inimitably Nina: the dark shades in I Can’t See Nobody became overtly political. Diana was inimitably Diana, effervescent with the Supremes, silk and velvet on her own.

But Aretha was all this and more. The New York Times put it well on Friday: “sensual and strong, long-suffering but ultimately indomitable, loving but not to be taken for granted”. She wore her personal story rather than reveal it; she exuded womanhood rather than sexuality. She cried the cry of freedom and liberation for her fellow women and people with a level of voltage, exhilaration, energy, sweat and tears and, yes, Soul – again, all three definitions – that surpassed those around her.

The air was thick with mercurial intoxication, as well as purpose, that night in Hammersmith; the mind’s eye neither can nor will ever forget Aretha’s inflammable but all-too-human presence on stage, nor will the middle ear recover from the impulsive, sometimes poignant presence of that voice.

Smokey Robinson used that term on CBS television yesterday: asked what we’ve lost most, he replied “her presence”. Aretha’s most obvious follower Stevie Wonder said: “I thought I’d cried my last tear” before visiting Aretha shortly before she died – but he was wrong. He’d heard her sing in church, he said, when he was four or five. He said the voices he remembered most in life were Dr King’s, Aretha’s and that of her father. The liberator-leader, the preacher-activist – both shot dead - and the singer who gave their message soul, and whose ‘Best of’ Atlantic Records LP I have been playing (like anyone else attempting to harbour a soul) all weekend: ‘Think’ – side 1, track 3 – at full volume, then ‘Respect’ side 2, track 1.

'When Words Fail’ – Aretha!

Ed Vulliamy talks about his new book, When Words Fail – A Life With Music War And Peace, at the Edinburgh International Book Festival on Tuesday, August 21 at the Spark Theatre, George Street. The book is published by Granta on September 6.