Things are different in the deep, rural South. One example, and there are certainly plenty more, is that Sunday is the biggest party night in many of the little slapdash clubs where the blues is performed. Those evenings, when the booze runs like water and the musicians play as if that were the only way to put out a fire licking at the seats of their pants, are the week’s last explosion of liberty for the patrons. Most of them are poor African-Americans, and come Monday morning they’ll be tying into five or six long, hard days of tending fields in the sun, gutting thousands of pounds of farmed catfish, inhaling fibers in a cotton gin, or doing some other back- and spirit-breaking job.

On many Sundays, it’s singer/guitarist Willie King’s job to provide their temporary elevation. And on many Sundays, he can be found fulfilling his duties at a little northwest Alabama joint near his home called Bettie Jean’s. But the music, or at least the words you’ll hear spilling through the cracks in Bettie Jean’s walls, are unlike almost anything else you’ll hear from Alabama to the Mississippi Hills and the Delta and up through the Piedmont. In a warm voice that sounds caked with decades of smoke and phlegm — a true voice of experience — King sings real freedom songs. His most pointed numbers are about social injustice and the struggle for racial unity, and they’re backed by his 40 years of community work and civil-rights activism. And by his easy musical sensibility, which is captured in all its rough perfection on his recent Living in a New World (Rooster Blues), where he’s supported by his usual Sunday-night crew, the Liberators.

King, who plays the House of Blues in Harvard Square this Monday, has a knack for plucking raw tones and pushing sweetly upswept notes out of his Stratocaster guitar. And for building simple one-chord and 12-bar frames for complex issues. Not that he’s always heavy. After all, his job is to inject some helium into his regular listeners’ lives. In the service of which he’s got tunes like the blasting romp "The Stomper," an ode to a lead-footed regular at Bettie Jean’s, and "You So Evil," a growling tribute to Howlin’ Wolf. Even as he begs "Will you please hear my call/America, let’s come together" in "America," the groove slinks around the dance floor and gets goosed by a sugary six-string solo that fades into a symbolic coupling with a funky sax line. But the meat of the matter is numbers like "Terrorized," where, in the voice of a weary country preacher, he sings, "Talk about terror/Peoples I been terrorized all my days. . . . You took my name and you know you left me in chains/Wouldn’t let me go to school/And you know I couldn’t read or write. . . . They gave me the news/And they called me a fool. . . . You know they come around and hung me/Hung me from the tallest oak tree/And you talk about terror?/I been terrorized all my days." All the time, his guitar softly and delicately weeps along.

"I started writing on ‘Terrorized’ after 9/11," he explains over the phone from his home. "We sorry it happened, I sure am, but afterwards when everybody up there in the government was talking about bein’ terrorized and terrorism, I thought about the plantation days — how we were terrorized on the plantations. You know, we had to go through hell. Our people had nothing. We had to suffer and work hard for no money. You couldn’t hardly get no food to eat. I thought, ‘Well, this is also being terrorized,’ and it doesn’t seem like too many people had feelings for you then. If you were African-American, they didn’t classify you as human."

King, who was born in Prairie Point, Mississippi, in 1943, has been involved in fundraising for literacy and health-care initiatives, and he’s been agitating for voters’ rights and against segregation since the Martin Luther King era. "When people got together and decided they weren’t goin’ to take it no more, I needed to be part of that. My dream is for people of all kinds to come together in America and all over this world. I need to fight for that. I was born, man, to be a fighter in the blues, because that’s what the blues musician is supposed to be. The music came out of a people who was terrorized and oppressed. It was God’s gift to a people who was catchin’ pure hell. And it might be a long time before the music gets the job done, but while you’re waitin’, it just kind of ease your misery."

Willie King & the Liberators play the House of Blues this Monday, September 16, with local opener Sam Hooper. Call (617) 491-BLUE.