《周礼·冬官考工记·总叙》
天有寒温之时，地有刚柔之气，材质有优良的，工艺有精巧的：把这四方面结合起来，然后可以制作精良的器物。
天有时，地有气，材有美，工有巧，合此四者，然后可以为良。
Heaven has the time of cold and warmth, the earth has the nature of strength and softness, the materials have good and bad, and the craftsmanship has fine and rough: combine these four aspects, and then you can make fine utensils.