Between 1912 and 1914, Duchamp produced the Cubo-Futuristic The King and Queen Surrounded by Swift Nudes, and two versions of a schematic, proto-Pop rendering of a machine used by confectioners to crush cocoa beans (The Chocolate Grinder); the latter would later appear as the central element in his magnum opus, The Large Glass.

Meanwhile, in 1913, Duchamp mounted the front wheel of a bicycle to a stool vertically so it could spin freely. He told Tompkins that he kept it around his studio as a “a pleasant gadget.” In 1914 it was joined by a bottle-drying rack purchased at a Parisian department store, the Bazar de l’Hôtel de Ville.

With these objects,Duchamp crossed a Rubicon of art history, utterly changing the underlying assumptions about artistic practice. Now, anything could be art as long as the artist deemed it so. Duchamp took Braque’s and Picasso’s introduction of collage into painting to its logical conclusion, making concrete the leap from art to life.

Still, Duchamp didn’t fully appreciate what he’d done until a 1915 sojourn to New York, where he encountered a veritable Moloch of manufactured goods. This had the effect of clarifying the meaning of his “pleasant gadget.” In a letter to his sister Suzanne, Duchamp mentioned the bicycle wheel and the bottle rack, explaining that he’d also “bought some objects of similar taste” while in New York. “I will treat them as ‘readymade,’” he wrote. “I sign them and . . . then apply an English inscription.” He went on to cite one of his most famous works of this type, a snow shovel inscribed with “In advance of the broken arm,” and ended the letter by instructing Suzanne to sign the bottle rack back in Paris, “Après Marcel Duchamp.”

What followed was a string of Readymades, some of them altered or “assisted” by Duchamp. In one example, he scribbled a Van Dyke beard on a postcard of the Mona Lisa, then added underneath the image, “L.H.O.O.Q”—letters that, when sounded out in French, translate to “She’s got a hot ass.”

The most controversial Readymade of all, however, was a urinal turned upside-down titled Fountain, which Duchamp anonymously entered under the name R. Mutt to the inaugural exhibit of the Society of Independent Artists in 1917. Though the rules committee stipulated that any piece would be accepted as long as the artist paid a $60 entrance fee, it refused to allow Fountain into the show area—prompting Duchamp to walk out with it. Fountain subsequently appeared in a photograph by Alfred Stieglitz on the cover of the Dada journal The Blind Man, in which Duchamp offered a spirited defense of R. Mutt’s intentions. “Whether Mr. Mutt . . . made the fountain or not has no importance,” he wrote. “He took an ordinary article of life . . . [and] created a new thought for that object.” He wryly added that the piece was a celebration of America, whose only true artworks were “her plumbing and her bridges.”