 These difficulties have prompted some philosophers to avoid the moves that generate them. An early such attempt is Guy Rohrbaugh’s (2003) view that works of art are not abstract objects at all, but rather historical individuals—non-physical entities ontologically dependent on a physical series of historically and causally linked physical objects. For example, a photograph is a non-physical entity dependent on its “embodiments” in a negative and subsequent prints. In a more recent proposal, Christy Mag Uidhir (2013) argues that works of art must have authors, but that neither discovery, nor indication of abstract structures, nor existential dependence satisfies the requirements for authorship. He concludes that repeatable works of art cannot be abstract objects of any kind, but must rather be ordinary concrete objects. Their apparent repeatability does not mean that they are instances of an abstract work, but only that they bear relevant similarity to one another. In a related vein, Allan Hazlett (2012) claims that there are no repeatable artworks. If there were, he says, they would have to be abstract objects. But abstract objects have all their intrinsic properties essentially, whereas artworks typically do not. For example, Alvin Ailey’s major work, Revelations, premiered as a 10 section work lasting an hour, but evolved into a half hour long piece in three sections. So, clearly, many of its original properties were not essential to it. Hazlett concludes that apparent repetitions are not instances of an abstract object. They are either separate, similar artworks, or copies of an original.