What is art?
This is obviously a tough one, but I think that almost anything that is a human creation or the result of a creative effort could be called art. But perhaps it takes more than that: perhaps there has to be some kind of intent on the part of the creator. I'm not sure about this, though—if enough people judge the result to be "art," does the one who performed or created it have to have intended it to be seen that way? How self-conscious do you have to be?
How do we know it is art?
I'm not sure about this, either. As I mentioned above, perhaps all creative work has the potential to be art. Grayson Perry's lecture ("Democracy has bad taste") suggests that quality in art is arrived at by a tribe. Could the same hold true for judging whether or not something is art at all?
Who decides what is art?
I'm not sure there can be an ultimate answer to this, but the judgement of the tribe or guild might be one place to start. The challenge with any guild, though, is that can become a closed shop—once it decides who is worthy it can then close the door to new people, ideas or approaches.
Does intent matter when judging what is art? Is reception the key? Is it enough if I decide that my work is art, regardless of what everyone else thinks?
If the simple fact that an item appears in a gallery makes it art, all we have done is hand over judgement to the gallery owner. Perhaps that is a good place to begin, but he or she is just one possible source of validation. Would others then be swayed by the gallery, rather than thinking about the value of the work itself?
Duchamp's statement about wanting "to put art back in the service of the mind" makes me wonder what he is opposing. Does he think that art has been in the service of the emotions? of sentiment? of fashion? of settled opinion? Perhaps he viewed his art as an opportunity to provoke thought. If that's the case, he must have seen Fountain as a success: it is not immediately clear why the artist views this piece as art, how he can offer it as his own work, and what the viewer is supposed to take away from it. The viewer can either reject the piece outright or be forced to think about questions of meaning.