American Sublime, the Bowerbird-produced eight-day festival devoted to the counterrevolutionary composer Morton Feldman, one of the most curious figures to emerge from New York's postwar avant-garde, opened quietly Saturday. And it stubbornly remained that way at Rodeph Shalom with the composer's 100-minute piano work,

Triadic Memories

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Preparing in advance with scores and recordings did not necessarily make you ready for the experience that unfolded at the hands of Feldman specialist Marilyn Nonken.

Though the soft, slow-motion 1981 Triadic Memories has been dismissed as obscure pianistic noodling, the 70 or so listeners on Saturday seemed to meet the piece more than halfway (there wasn't a single cough) and were rewarded with a wide-awake dream, something like an extended visit with a brilliant, improvising somnambulist.

Usual musical signposts were nowhere to be heard. Nothing in the piece announced itself. Most of the motifs - simple handfuls of unimposing notes - had unexpected trapdoors that led into the next motif.

At times, Feldman broke away in contrasting registers from the organic development that came before.

Sometimes the music evolved into a single note, sounded repeatedly, though never seeming repetitious because the composer succeeded in going deeper into the note. When the piece lapsed into extended silence, the moments were heart-stopping.

No doubt Feldman's subtle means of unification aided in this effect. (There's nothing random about this music.) So did the near-miraculous alchemy of pianist Nonken.

Composed at a time when music had gone into esoteric realms that felt more scientific than artistic, Triadic Memories shows how Feldman retreated ever more determinedly into musical fundamentals. Never did the piece feel radical. Or right. Or wrong. Or good or bad.

It simply was. How well will this aesthetic wear over a series of concerts that is being called the biggest-ever Feldman festival? Will it be more of the same? Will anybody mind?

Contact music critic David Patrick Stearns at dstearns@phillynews.com.