Not the Wind, Not the Flag

Two monks were arguing about a flag. One said, "The flag is moving."

The other said, "The wind is moving."

The sixth patriarch happened to be passing by. He told them, "Not the wind, not the flag: mind is moving."

Wind, flag, mind moves,
The same understanding,
When the mouth opens
All are wrong.

-From the 13th century Zen text "The Gateless Gate" by Ekai, called Mumon