WOODY Guthrie, the Dust Bowl Troubadour, wrote This Land is Your Land in 1940, a year before he famously inscribed This Machine Kills Fascists on his guitar, and the political song has always been a staple of my music library, in a line from Guthrie down through, among many others, Bob Dylan, Bruce Springsteen, Joe Strummer, Elvis Costello and Robert Wyatt.

The vitality, heart and commitment which activism can bring to bear on music was brought to mind by this week's Oscar award to Common and John Legend for their magnificent anthem Glory, written for the film Selma, in which rap artist and actor Common plays one of Martin Luther King's associates.

The song is annoyingly thrown away during the closing credits of this wonderful film, so people are getting on their coats and dumping their popcorn tubs, but for the best live version look for the Grammys performance. The sound quality at the Oscars version is horrible but that is overcome, to coin that phrase, by the powerful acceptance speeches. Common's rap lyrics span the 50 years since the events in Alabama: "That's why Rosa sat on the bus/That's why we march through Ferguson with our hands up."

Rap's not usually my thing. Often there's too much loathing - of self, others, women and gays in particular - for my taste but Common rightly said the story of Selma "transcends race, religion, sexual orientation and social status," which warmed this heart.

John Legend was even more specific: "Selma is now. The struggle for justice is now. We live in the most incarcerated country in the world. There are more black men under correctional control today than there were under slavery in 1850." Not your standard Oscars fare, then.

Indeed political song has rarely featured at the Oscars. Bob Dylan won in 2000 for Things Have Changed, not one of his more polemical creations. Indeed, Dylan voiced a version of it for a protectionist advert for Chrysler cars during last year's Superbowl. No, the nearest to a protest song would be Bruce Springsteen lament for the plight of those infected by HIV in 1993, The Streets of Philadelphia.

But for an original protest song from the Boss you want to turn to his Live in New York City album and the track American Skin (41 shots). That was the number of bullets plain clothes NYPD officers put into unarmed 22-year-old Amadou Diallo in the doorway of his own home in 1999.

Springsteen had regularly done benefit concerts for fallen police officers, but when he wrote this song the police union rounded on him as a "faggot" (nice equalities touch there), even though the lyric is scrupulously observant of the doubts and dilemmas when someone reaches for a pocket - "Is it a gun, is it knife, is it a wallet, this is your life."

The next track on the same album, Land of Hope and Dreams, is also a hymn to "saints and sinners, losers and winners, whores and gamblers, lost souls, the broken hearted, lost souls departed, fools and lost kings" where "faith will be rewarded". But there are, of course, "bells of freedom ringing". Good luck unravelling that, but you feel Woody would have approved.

It will be less certain that he would have approved of The Clash but Joe Strummer - from Tommy Gun and Clampdown to I Fought the Law - was a huge admirer of Guthrie and he would have understood Gil Scott-Heron on Vietnam, or even Billy Joel's Goodnight Saigon.

Everyone marches with the voices of their own heroes. Elvis Costello was condemned for the starkness of his anti Thatcher rant Tramp the Dirt Down, but his Falklands War-inspired Shipbuilding is incomparable. The version by Northumbrian folk sisters The Unthanks looms large and they connect again in my music library, for they covered Robert Wyatt's Out of the Blue, which he co-wrote with his wife Alfie Benge in response to Israeli bombing of refugee camps.

But the song which remains constantly on my playlist is The Unthanks version of Wyatt's Free Will and Testament. A supremely talented drummer with progressive rock group Soft Machine, Wyatt broke his back in a fall but never faltered in his commitment to music, which continues at the age of 70.

In this astounding song he asks, what is free will? What is control over your own life and destiny? "Is there freedom to un-be?" he writes. "Is there freedom from will-to-be?" There is a protest lyric I'd force MSPs to listen to as they ponder Margo's Bill on assisted suicide and the freedom to un-be.