Chapter 1: Classification is a universal human attirbute. There seem to often be two categories.
Traditional Micronesians seem to classify living things into two groups: Animals and Plants. But remember how german classifies the noun "maedchen" (maiden) as neutral, taking the neutral article "das"? Chuukese does something like that with counting classifiers. English uses counting classifiers trivially; but other languages incorporate explicit syntactic rules for applying them. In Chuukese, the classifier is obligatory (or WAS, because younger speakers don't learn their more sophisticated aspects).
The classifier for a long skinny item is "foch". Like a stick of gum, efoch gum = one stick on gum. ruefoch gum = two sticks of gum.
The classifier for an animal is "men". Emen pik = one pig; emen mwan = one man. Ruemen pik = two pigs, etc. But interestingly, for the octopus, ew kuus = one octopus, it is not given the classifier for animals!
And then, here's a stranger one still, I think: a saw or a knife IS given the classifier "men": Emen ngerenger = one saw.
Chapter 2: Early thinkers also posited two higher categories.
More to come