Intermission chatter at Wednesday's Christian Zacharias recital took on ominous tones when one sage pianophile observed, "He tends to take things to the extreme."

And what makes Zacharias one of the most fascinating elder-statesman keyboard personalities is that you never know which extreme he'll take. Or if you're going to like it. Possessed of effortless technique, decades of accumulated repertoire, huge intellect, and wide-ranging imagination, he has options.

The first half of his Philadelphia Chamber Music Society concert at the Kimmel Center brought together C.P.E. Bach at his craziest, Brahms at his most reflective, and Beethoven's late-period Piano Sonata (Op. 110). Thanks to Zacharias' singular insights, he showed how the music from this unlikely trio was all of a piece.

Coming from a father (J.S. Bach) who had spent his life reconciling musical seams with two books of The Well- Tempered Clavier, Carl Philipp Emanuel (1714-88) bounced between conforming to fashion in court-musician appointments and acting out in keyboard pieces whose modulations lunged into the most distant left field imaginable. He found his muse not in order but in disassemblage, in the juxtaposition of fragments. What makes him more obscure than visionary is that he often seemed unable to sustain a musical argument of any length, making his pieces more like musical exclamations than works of art.

The art part came only 40 years later with Beethoven. What were musical non sequiturs in the hands of C.P.E. became Beethoven's most intensely chiseled monuments, ones that required generations to be understood.

The fact that Zacharias put Brahms between the two - as opposed to following the usual chronological order - shook you out of your usual points of reference with that composer. The four works from his Op. 119 were played in a loose-limbed fashion, often with slowish tempos, making you aware of the many moving parts (and not necessarily congruent ones) that lie beyond the pieces' appealing melodies.

The performances were unlike anyone else's. With his clean, fleet clarity, Zacharias made the Bach Piano Sonata in A minor and Rondo in C minor as scintillating as Domenico Scarlatti so that when the music fell through one of many trap doors or came unhinged, the effect was all the more jaw-dropping. Brahms is usually played with dark timbres; Zacharias made the treble lines speak more clearly within an evenly voiced harmonic spectrum. Though late Beethoven is often played like a Zen koan or platform for abstract philosophy, Zacharias played Op. 110 purely and simply, as a thing of beauty. I could have done without some of his overly elastic rhythms, but the overall package is likely to glisten at length in my memory.

The second half - Schubert's Piano Sonata in D major (D. 850) - seemed not to be part of the rest of the program's concept, especially in a performance that was unsentimental in the extreme. Zacharias' cool sonorities assured you would hear no echoes of the vocal harmonies that informed so much of Schubert's piano writing. Melodies were brushed by quickly, without reference to their emotional content. What emerged in the process of elimination was the musical architecture, and in this particular 1825 piece, that aspect isn't extraordinarily interesting. The sonata goes on and on and on. The question in any given performance is if you mind. In this one, I minded a lot.

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