About three-quarters of the way through Vallée d’Obermann, the anchor of the first book of Franz Liszt's Années de pèlerinage, the pianist is confronted with a difficult choice: either play the reading given in normal type at measure 181 and following (ex. 4.1) or select the one above it in slightly smaller print marked “ossia.” At first glance, both passages seem to share much in common, including sonorous, open-position right-hand chords and expansive left-hand arpeggios. As each passage develops, however, the differences start to outnumber the similarities. The “ossia” passage introduces accidentals in measure 182 that give the ethereal melody a decidedly melancholic character, while the other remains decidedly in the tonic; only later, at measure 183, does it seem to catch up.

Yet, by that point, the ossia has not only moved much further afield harmonically, but it has also returned to interrogating the piece's main motive, which Liszt has already presented in several clever permutations. Above this primal motivic reprise floats a new arpeggiated figure that seems to have developed out of the preceding left-hand accompaniment and is keen to run through chains of characteristic Lisztian thirds. Meanwhile, the passage in regular type has introduced a hypnotic, oscillating right-hand triplet accompaniment whose high altitude on the keyboard underscores the plaintive features of the melody—another rendition, this time in inversion, of the ubiquitous falling motive—that lies beneath.

To be sure, today it is relatively uncommon to find ossia passages in printed music. Rachmaninoff has a famous one in his Third Piano Concerto, op. 30, as does Beethoven in the first movement of his Fifth, op. 73. Ossia passages can help pianists negotiate some of the thornier spots in Brahms's Piano Sonata in C Major, op. 1, or Glazunov's “Sascha” Suite, op. 2; on the flip side, they can also enhance a performer's virtuosic credentials by providing more difficult or showy readings of shopworn music.