Full Idea
By knowing one lump of clay, all things made of clay are known; by knowing a nugget of gold, all things made of gold are known.
Gist of Idea
By knowing one piece of clay or gold, you know all of clay or gold
Source
Anon (Upan) (The Upanishads [c.950 BCE], 'Chandogya')
Book Reference
'The Upanishads', ed/tr. Prabhavananda /Manchester [Mentor 1957], p.68
A Reaction
I can't think of a better basic definition of a natural kind. There is an inductive assumption, of course, which hits trouble when you meet fool's gold, or two different sorts of jade. But the concept of a natural kind is no more than this.
Related Idea
Idea 6939 What is true of one piece of copper is true of another (unlike brass) [Peirce]