Knowns and Unknowns

I've been thinking a lot about how what we know changes as we age.  It's a truism that the young know everything, and only find out they're wrong when they're older, and then come to think they may not know anything, but that's not true.

Following Rumsfeld's categorization of knowledge, we have this system:

1. Known Knowns (things we know we know)
2. Known Unknowns (things we know are out there, but we aren't sure of what exactly they are)
3. Unknown Knowns (things we know but are not aware of knowning -- covert categories of knowledge)
4. Unknown Unknowns (things that we know nothing about and don't even suspect are out there)

I suppose that when we age, we recognize that  Category 4 exists, that it's larger than we thought, and that Category 1 is smaller than we thought.    Number 3 is interesting to me as an anthropologist, because it represents our cultural biases and worldview.  The concept is discussed in folk taxonomy research.