Many great songwriters—Dylan, Cohen, Mitchell, Prine—secure their places in history through an oeuvre, but the rare few do it with a song or two. Iris DeMent is one, with a pair of compositions—1993's much-covered agnostic hymn "Let the Mystery Be" and 1994's miraculous song-about-songwriting "Sweet Is the Melody"—so pure and good (conceptually, lyrically, vocally) that they'll be revered for as long as white folks take up acoustic guitars. In 2003, DeMent made headlines by swearing off performing while the US waged war in Iraq. Tonight, she returns to the Seattle stage, with opener Rachel Harrington. (The Triple Door, 216 Union St, www.thetripledoor.net, 7:30 pm, $35 adv/$38 DOS, all ages)