From Jorge Luis Borges' description of a fictional Chinese classification of animals:
“These ambiguities, redundancies and deficiencies remind us of those which doctor Franz Kuhn attributes to a certain Chinese encyclopaedia entitled 'Celestial Empire of benevolent Knowledge'. In its remote pages it is written that the animals are divided into: (a) belonging to the emperor, (b) embalmed, (c) tame, (d) sucking pigs, (e) sirens, (f) fabulous, (g) stray dogs, (h) included in the present classification, (i) frenzied, (j) innumerable, (k) drawn with a very fine camelhair brush, (l) et cetera, (m) having just broken the water pitcher, (n) that from a long way off look like flies.” Jorge Luis Borges, Other Inquisitions: 1937-1952
The lesson? That a system of classification needs to rest upon a coherent, logical assessment of the causal and structural properties of the things being classified, so that the classification may lead us to a better understanding of the range of phenomena encompassed by the system.