There is a property of words analogous to the wave – particle duality that exists in physics. In physics, it’s simply a point of view and interaction whether a physical entity behaves like a wave or a particle. Similarly, an essential concept can be expressed as (and in the form of) a noun, a verb, or a descriptive adjective. In other words, under each set of semantically related noun – verb – adjective tuples lies an essential concept.

When examined, we find that each essential concept has a root expression as a noun, a verb, or an adjective. The expression of a concept begins in one of these three word classes. However, by appending appropriate suffixes (or a prefix), each of these three word classes can be transformed into another.

Thus, the underlying concept can be said to be independent of any specific word class. Alternatively, we could say that all three word classes (noun, verb, and adjective) taken together provide the fullest expression of an essential concept.

This principle has significance for object-oriented conceptual modeling. We want to find useful (usable) subjects and objects, domain objects with usable faces. The principle of conceptual equivalence allows us to reshape statements until they are usable for building conceptual models, especially models that focus on objects (nouns) and associated facets (constellations of verbs).