In the opinion of Germaine Greer, the better kind of art is that which one cannot collect. Therefore, since one can collect the works of, say, Hogarth, Rembrandt, Turner, or Caravaggio, she must think them necessarily inferior to works such as Martin Creed’s The Lights Going On and Off, an uncollectable work to which I presume Professor Greer alludes in the following passage:
The artist positions you in a dark room and turns the light on, and off again. He does no more because there is no need to do more. In finding yourself equal to the encounter, you are empowered with the artist’s own intellectual energy. For the time you are together, you are sharing the same cerebral space. 
If she really finds herself intellectually stimulated by a light going on and off, one might suggest she take up a vocation more suited to her level of intellect, though, considering that she now frequently writes opinion-pieces for the The Guardian, one might suspect she has already found it.
 Germaine Greer, “Here’s a message for the art mafia in their black Bentleys: the really good stuff is uncollectible”, The Guardian, 23rd October 2006.