We observe the entities of the world, develop ideas about them, form concepts based on our observations. To share our ideas with others, we express them in a language, representing them verbally, pictorially, symbolically, or even musically. To be meaningful, the representation must have a referent which may be any entity tangible or abstract: an existing or planned object, a situation, an idea, a theory, a person or group, a business, an emotional state. Poems, novels, paintings, top secret documents, a pay cheque, files placed on the internet for general access, the carvings on the Rosetta Stone are all representations of existing entities or of ideas of their creators, as are architectural drawings, road maps, specifications and admiralty charts.

Real-life entities can give rise to a wealth of different observations. The expression of these preserves some features of the referent while suppressing others. Unscrupulous vendors, dishonest advertisers, sharp operators might describe their wares in flowery language while exaggerating or being economical with the truth. They might choose attributes tendentiously, or distort the report of observations deliberately. By contrast, scientists, engineers, problem solvers are obliged by the ethics of their profession to be concise, focus on facts, select attributes most relevant to the purpose, convey observations without bias and as accurately as possible, and be explicit about the bounds of validity. A good representation is a purposeful, honest, dispassionate portrayal of the referent.