The folk theory is what we all have about what objects are like. A lot of science consists of looking for essences of things, for instance the essences of molecules or species. The folk theory of essences fails a lot in the real world, but it structures our understanding of categories. We assume there are essences even if we don't know them and that there are experts who can test for the essences. Radial categories are very complex, particularly interesting categories, which we do not know how to characterize in a neural system.
Radial categories are everywhere.
They example of a radial category from the reading is 'mother'. The typical cases of mother are defined by the birth frame, the nurturance frame, the genetic frame, the marriage frame and the anthropological frame. In the central case, all of these frames apply, but in many cases only some of the frames apply, as in 'step mother'. In some cases only one model is satisfied. For instance, the woman who donates genetic material to a child, but doesn't give birth to it or raise is it is a kind of mother which satisfies only the genetic model.