"Thirty spokes meet at the hub,
But the void within them creates the essence of the wheel.
Clay forms the pot,
But the void within creates the essence of the pot.
Walls with windows and doors make the house,
But the void within them creates the essence of the house.
Fundamentally:
The material contains utility,
The immaterial contains essence."
Attributed to Lao-tse, quoted by Johannes Itten for the opening of the first student exhibition at his Berlin school, 1918.
