Robert Motherwell (1915-1991), one of the leading American Abstract Expressionist painters, was also a theorist and exponent of the movement. His writing articulated the intent of the New York school -Jackson Pollock, Willem de Kooning, Adolph Gottlieb, Franz Kline, Arshile Gorky, and others-during a period when their work was often reviled for its departure from traditional representation. As founder of the Documents of Modern Art series (later renamed...