exist in some quantity, but may exist in any quantity."

Rand argued that concepts are organized hierarchically. Concepts such as 'dog,' which bring together "concretes" available in perception, can be differentiated (into the concepts of 'dachshund,' 'poodle,' etc.) or integrated (along with 'cat,' etc., into the concept of 'animal'). Abstract concepts such as 'animal' can be further integrated, via "abstraction from abstractions", into such concepts as 'living thing.' Concepts are formed in the context of knowledge available. A young