The Isley Brothers pioneered begging, a skill later appropriated by everyone from Al Green to Biggie Smalls (via sampling, but still). Frontman Ronald’s voice is thick and light all at once, fluttering atop electric-guitar soul (the Jimi Hendrix–inspired “That Lady”) or grimy funk vamps (“It’s Your Thing”). It also invigorates easy-listening R&B (“Summer Breeze,” originally a hit for Seals & Croft), giving punch to lines that would merely wobble out of a lesser mouth. There’s no filler on this double-disc set — even the disco relics (“Take Me to the Next Phase”) are revelations. And while the backup Isleys are formidable (especially Ernie on guitar and drums), Ronald sounds not a day older on R. Kelly’s 1995 pimp march “Down Low” than he did on 1975’s “Make Me Say It Again Girl.” The student should have learned a lesson from the teacher: Some beauty ages perfectly.

DOWNLOAD THESE “This Old Heart of Mine,” “Between the Sheets,” “Summer Breeze”