From Alan Watts' What is Zen?:
There was once an Englishman and an Indian sitting in a garden together, and the Hindu was trying to explain basic Indian philosophy to the Englishman. So he said, "Look now, there is a hedge at the end of the garden - against what do you see the hedge?"
The Englishman said, "Against the hills."
"And what do you see the hills against?"
He said, "Against the sky."
"And what do you see the sky against?" And the Englishman didn't know what to say.
So the Hindu said, "You see it against consciousness."