The Bellows That Never Collapses
Compares the space between heaven and earth to a blacksmith's bellows, whose emptiness is exactly what allows it to keep producing without ever running dry.
In the middle of chapter 5, after the straw-dogs image, Laozi asks: "is not the space between heaven and earth like a bellows?" A bellows — the accordion-like tool used to pump air into a forge — is defined by being hollow; it does nothing when full or rigid, and everything when it's empty and free to move. The chapter observes that it is "empty yet never depleted; the more it moves, the more it produces" — the harder it's worked, the more it gives, precisely because it isn't stocked with a finite reserve that could run out. This image sits alongside the valley of chapter 6 and the vessel of chapter 11 as one of the text's recurring proofs that emptiness is generative rather than deficient. The bellows also sets up the chapter's closing advice to "hold to the center," since a bellows only works when its cavity stays open and unobstructed, not when it's forced or overworked at either extreme.
Empty yet never depleted; the more it moves, the more it produces.
Tao Te Ching