The problem with categories, at least as proposed by Kant, is that they are inescapable pre-existing conditions, if you will, and all perception MUST BE filtered through them.The categories take priority and, in effect, determine what we see and how we see it. These categories reflect the fact, according to Kant, that knowledge comes from theoretical deduction and not sensory experience or observation. Now, without getting too heavy or into that specific debate, I just want to point out that frames around art often suggest just the opposite, that we are about to enter a world where pre-existing conditions, so-to-speak, are about to be questioned or even denied or defied. As well, we may be entering a world where sensation and observation are more primary than thought and understanding. The frame can be seen as an invitation to a more immediate kind of relationship to what we see and hear than what would typically be allowed by a necessary filtration through already-known categories. Consider Warhol and his soup cans or Duchamp's mustache on the Mona Lisa. They actually defied the category of art itself. Sometimes, a frame acts more as a WARNING than a border or container!