Pianist Easley Blackwood, who's taught at the University of Chicago for more than three decades, is something of both a recluse and an eccentric. His reclusiveness may explain why he rarely gives solo recitals and is only an occasional member of the Grammy-winning Chicago Pro Musica. His eccentricity surely accounts for his choice of repertory, with its disproportionate share of unclassifiable and gleefully difficult late-19th-century and 20th-century pieces. Take the centerpiece of Blackwood's first solo appearance in many a year: Ives's Second Sonata, subtitled "Concord, Mass. 1840-1860." The notoriously demanding work--a complex web of ideas under the guise of musical sketches of transcendental thinkers Emerson, Hawthorne, the Alcotts, and Thoreau--daunts most pianists. (The last live performance of it I heard, in fact, was given by Blackwood more than 15 years ago.) Having devoted years to learning the music, Blackwood arguably is the only interpreter who's managed a lucid and coherent account (now available on the local label Cedille Records). Also on the bill are Sonatina (1916), an ersatz avant-garde fancy by the influential Italian composer Alfredo Casella, and Karol Szymanowski's Masques (1916), whose movie-music essence is heightened by episodic allusions to Scheherazade, Tristan, and Don Juan. Blackwood will return in a joint recital (with cellist Kim Scholes) on February 21 performing Frank Bridge's Sonata (1917) and his own (1985), among others. Tonight at 8; Mandel Hall, University of Chicago, 1131 E. 57th; 702-8068.