What Realm Does the Echo in the Valley Belong To?

If you shout loudly in a valley, that sound is the essential realm (the original sound). When this essential realm encounters the air or a stone wall and meets with obstruction, the propagated sound becomes altered in quality, because the four great elements—the material particles—have undergone change. When we then hear the echo, the sound feels rather illusory and unreal, as if it came from a distant horizon, greatly different from the person's shout. The person's shout is real, whereas the echo arises afterward, transformed on the basis of the shout—just like a second moon.

The echo is similar to a sound rebounding upon meeting an obstruction, like a ping-pong ball rebounding off a paddle; the speed of the rebounding ping-pong ball is determined by the magnitude of the resistance it encounters. The volume and sound quality of the echo in an empty valley depend on the force of the air convection and the magnitude of the resistance from the stone walls. The more open and empty the valley, the more false, illusory, and unreal the echo becomes. The echo in a valley can neither be said to be real nor said to be false; it possesses a nature that is both real and unreal, because it carries the substance of the essential realm.

The second moon comes directly from the true moon in the sky—the first moon. Without the first moon there would be no second moon. You cannot say the second moon is real, nor can you say the second moon is false. The second moon possesses a nature that is both real and unreal, because it carries the substance of the essential realm of the first moon—and it carries quite a lot of it, which is why it appears rather real. Even so, a person of wisdom, when pinching out a second moon, will not take it to be the real first moon. By the same token, one should not mistake the echo in an empty valley for the real voice of a person; one can only follow the echo to seek the person's real voice, and thereby find the person. This is also the secret of investigating Chan (canchan).