Let’s begin with the obvious: Duchamp’s Fountain really was a urinal. Not a painting or sculpture of a urinoir – though the latter might raise interesting philosophical questions – but the real thing, a token of a particular type – there were many visually indistinguishable urinals that came off the same production line. And just as importantly, Duchamp had no involvement whatsoever in designing or making the urinal that was the raw material for his artwork. His contribution was to sign the urinal, and exhibit it as art.

Source: It is and it isn’t | Marcel Duchamp’s ‘Fountain’ is not just a radical kind of art. It’s a philosophical dialetheia: a contradiction that is true