With the arrival of this holy trinity of American music, the wise critic should pass over it in silence because the music the three have produced surpasses understanding: Tony Rice, incontestably among the most eloquent guitar players to draw breath; Peter Rowan, a songwriter and singer worthy of mention with Jimmy Martin and Carter Stanley; and Vassar Clements, who ... oh, forget it. The show has been sold out for months anyway. If you don't have a ticket and are too broke to scalp, or if you're just curious about that limpid acoustic sound you've heard from higher-profile musicians such as Mark O'Connor and Alison Krauss (who, in a curse of scheduling, appears at Powell Symphony Hall the same night), then find Clements' 1973 Rounder debut, Crossing the Catskills, a classic of hillbilly fiddling, or his more recent swinging jazz album Back Porch Swing. His bow work, as recognizable and rare as a Botticelli brushstroke, glows and flows with the freedom of genius. Want to hear bluegrass singing as big and bright as a harvest moon? Find Rowan's New Moon Rising, a collection of original songs that solidified his reputation as a killer voice and writer, or comb the bins for Dust Bowl Children, the best politically charged album any bluegrasser ever made. And Rice? Get them all, every last disc. Before a physically ravaged voice sent him into semiseclusion, Rice's singing, with its immaculate tone and down-home ease, was his secret weapon and the unheralded key to the New South, the greatest bluegrass band of the 1970s. His flat-picked guitar, on the other hand, has continued to communicate deeply and wisely, without a single sung word. His damaged vocal cords may still be healing, but his playing has remained nimble, lyrical and (finally) incomparable. With one ear tuned to the bluegrass and old-time source and another to jazz freedom, Rice -- like Rowan and Clements -- remains as adventurous and inviolable an artist as any critic might dare imagine.