The Grove Dictionary of Music defines the word “aleatory” as follows: “A term applied to music whose composition and/or performance is, to a greater or lesser extent, undetermined by the composer.”

But isn’t music supposed to be organized, planned, determined sound? Isn’t “aleatoric music” a contradiction in terms? Well, not necessarily. Musicians throughout the ages have delighted in spontaneous, improvised sound, or musical games in which the results will be different with each performance.

In the 20th century, American composers like Charles Ives and Henry Cowell often gave performers a great deal of freedom in the realization of their scores, and John Cage developed what he called “chance operations” into an art form all its own.

On September 13, 1986, at Avery Fisher Hall in New York City, Leonard Bernstein conducted the Israel Philharmonic in the premiere of his new Concerto for Orchestra subtitled “Jubilee Games” which incorporates some aleatoric or chance elements. Bernstein’s Concerto is dedicated to the Israel Philharmonic on the occasion of its 50th anniversary jubilee.

Bernstein explained, “Its first movement is musical athletics, with cheers and all. It is also charades, anagrams, and children’s counting games. But mainly it is celebratory, therefore spontaneous, therefore aleatoric, ranging from structured improvisation to totally free orchestral invention. It is thus inevitable that the movement will vary considerably from one performance to another, and even one rehearsal to another.”