Thirty spokes converge on the wheel's hub. But the center emptiness of the hole which allows the wheel to function.

We make a vessel from a lump of clay; It is the empty space within the vessel that makes it useful.

We cut out doors and windows to make a house; and it's on inner spaces where there's nothing that the usefulness of the house depends.

Thus, while the tangible has advantages, It is the intangible that is for usefulness.useful.

 第十一章用无利有

三十辐，共一毂，当其无，有车之用。埏埴以为器，当其无，有器之用。凿户牖以为室，当其无，有室之用。故有之以为利，无之以为用。

[译文]

三十根辐条连接一个车毂之上, 有了车毂中空的部分，才有车的使用。和泥制成器皿，也恰恰是由于有器皿其中空部分，才有器皿的使用。建造房屋，开凿门窗，亦是由于门窗及四壁构成的空间，才有房屋供人使用。

因此，显现有形的宇宙万物给人带来便利，而无形的空才是获得使用价值的基础。