from 'Thud!' by Terry Pratchett
Fred Colon hesitated here. He knew in his heart that spinning upside down around a pole wearing a costume you could floss with definitely was not Art, and being painted lying on a bed wearing nothing but a smile and a small bunch of grapes was good solid Art, but putting your finger on why this was the case was a bit tricky. `No urns,' he said at last.
`What urns?' said Nobby.
`Nude women are only Art if there's an urn in it,' said Fred Colon. This sounded a bit weak even to him, so he added, `or a plinth. Both is best, o'course. It's a secret sign, see, that they put in to say that it's Art and okay to look at.'
`What about a potted plant?'
`That's okay if it's in an urn.'
`What about if it's not got an urn or a plinth or a potted plant?' said Nobby.
`Have you one in mind, Nobby?' said Colon suspiciously.
`Yes, The Goddess Anoia  Arising from the Cutlery,' said Nobby. `They've got it here. It was painted by a bloke with three i's in his name, which sounds pretty artistic to me.'
`The number of i's is important, Nobby,' said Sergeant Colon gravely, `but in these situations you have to ask yourself: where's the cherub? If there's a little fat pink kid holding a mirror or a fan or similar, then it's still okay. Even if he's grinning. Obviously you can't get urns everywhere.'
 Anoia is the Ankh-Morpork Goddess of Things That Get Stuck in Drawers.