A network of categories according to which data is organized and interpreted.
One way to understand reason is to perceive it as a mass of formless, inert matter on which objects and events are imprinted.
Another way is to see it as an internally structured, dynamic organ.
Thus, the categorical scheme is a network of principles through which the mind structures or organizes its data. However, to talk about a scheme means to focus not on the isolated categories, but on the internal connections between them, ie. on the ways in which these principles of organization work.