The iconic status of Arrangement in Grey and Black, No. 1 isn’t just because it marks “the peak of Whistler’s radical method of modulating tones of single colors.” It’s because, like Mona Lisa, The Scream, and American Gothic, “Whistler’s Mother” is “the distillation of a meaning instantly recognized and forever inexhaustible. In this case, it’s the mysteries of motherhood. Everybody has a mother, and something close to half of everybody becomes one.”