Spain’s most important museum has finally dedicated a retrospective to one of the most peculiar artistic groups to have surfaced in this country. Formed in July 1964 in Madrid by Juan Hidalgo, Walter Marchetti, and Ramón Barce, the group chose as its name a made-up, meaningless word—“ZAJ.” In 1956 Hidalgo and Marchetti met John Cage, an event that greatly contributed to the open-endedness of ZAJ’s actions, and in 1970 Esther Ferrer joined the movement, thus completing the most famous—yet most difficult to define—artistic group in contemporary Spain.

In the somber, repressive panorama of the Franco