There is, perhaps, one universal truth about all forms of human cognition: the ability to deal with knowledge is hugely exceeded by the potential knowledge contained in man’s environment. To cope with this diversity, man’s perception, his memory, and his thought processes early become governed by strategies for protecting his limited capacities from the confusion of overloading. We tend to perceive things schematically, for example, rather than in detail, or we represent a class of diverse things by some sort of averaged “typical instance.