So, the shopping trolley is a "ready-made", it is out of context (unless a diver has been collecting a lot of kelp), and therefore it is art. Except it isn't. Because whoever threw it into the water did not intend it to be seen as art, and did not deliberately organise it in the way I saw it. However, my photograph might be art! Because I do intend it to be seen that way, and I am presenting it to you as such!
All joking aside, Duchamp is the artist ultimately responsible for the question, "What is art?", being so difficult to answer. Up until the start of the twentieth century both artists and the public had a fair idea of what constituted art, and their definitions were broadly similar - give or take the odd Impressionist or Whistler spat! Since Duchamp that hasn't been the case. Consequently I assert that my photograph is art (pretty bad art I agree), and, thanks to Duchamp, it's hard for you to gainsay me!
photograph & text (c) T. Boughen