I have to disagree. I can't see any especial need for artists of the Edwardian period to reflect on the nature of art in quite the reductive way Duchamp did. When you consider who was painting, sculpting, printmaking, or designing buildings at the time, it is hard to see the period as one of stagnation that needed to return to its ontological roots in order to move onward. The late Victorian and Edwardian periods were one of the richest in history stylistically, with movements cross-pollinating across Europe, the Americas, Australia, the Orient, etc., and with many discredited or obscure styles reevaluated, and often reintegrated into modern work. Life was too short for them to meditate on the smallest unit of art.

Is your point that the smallest unit of art is the act of selection? More precisely, the act of selection for the purpose of communication? Yet there are different forms of communication, and it does not help to confuse them with art. A scientific statement is a form of communication about the state of things in the world, involving a great deal of selections, but it is not art. Duchamp's urinal was much the same kind of statement, but a statement of art theory rather than science. Apart from the fact that Duchamp had no hand in the design or execution of the urinal, so was in no way responsible for its intrinsic aesthetic form. All he did was make a kind of statement, one of juxtaposition, not even on the level of simile or metaphor (there's no synthesis or analogy). There is a skill of arrangement - and in the old vocabulary, an art - but the picture hanger had more of it than Duchamp, and greater integrity.

Perhaps the problem is the tendency of theorists to seek out a single definition or essence of art. I prefer to think of it as a dialectic. Art for me isn't just skill, or just design, or just ideas, but all three together; the art exists in the state of fusion of these elements. It requires skill to make a clear statement about the world, and you might use it to express ideas, but without a sense of design, it is not art. Skill and design together can make beautiful objects of craft, but without the ideal dimension (poetry, mood, feeling, thought) it is not art. The theoretical mind abhors this kind of cognitive instability, and wants art to be one thing or the other, instead of a special condition that arises out of both acting dialectically.

Just a thought,
Iian