There are artists who, although not perhaps of the very highest order, nonetheless define issues and create a vision so central to the aesthetic dilemmas of their time that they come to occupy a place and to exert an influence out of all proportion to the scale of their actual achievement. Kurt Schwitters, whose work is currently the subject of a major retrospective exhibition, is a figure of this sort.[1] At once immensely gifted and possessed of a quirky, original intelligence, he was also curiously limited in the principal endeavors of his career. Schwitters’s limitations, moreover, were neither inadvertent nor involuntary. They were deliberately chosen, and remained crucial to what he achieved. His special quality is therefore to be found almost as much in what he refused as in what he embraced. He is one of the authentic “little masters” of the modern movement, yet...