The Role of Definition for a Conceptual Being
Language allows a conceptual being to concretise his concepts, to achieve the full power of concept formation, the language cannot be merely ostensive. Man requires definition. “[Definition] is essential to every concept except axiomatic concepts and concepts denoting sensations.”1 For such perceptually self-evident concepts, all that is required–and possible–is to point to instances. “By green, I mean this; by red, I mean this,” etc. At the level of the perceptually-given, the concepts are automatically related to reality because a sense perception is a direct awareness of a concrete.
As one acquires a greater conceptual apparatus at ever increasing levels of abstraction, however, this is not sufficient. It is possible for man to err, to make false generalisations, to detatch his cognition from reality constructing a web of floating abstractions. To avoid this, man needs a method to explicitly identify the essence of a concept’s units—this is the role of definition.
If a concept is to be a device of cognition, it must be tied to reality. It must denote units that one has methodically isolated from all others. This, in Ayn Rand’s words, is the basic function of a definition: “to distinguish a concept from all other concepts and thus to keep its units differentiated from all other existents.”
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A definition cannot list all the characteristics of the units; such a catalogue would be too large to retain. Instead, a definition identifies a concept’s units by specifying their essential characteristics. The “essential” characteristic(s) [are] the fundamental characteristic(s) which makes the units the kind of existents they are and differentiates them from all other known existents.2