A popular understanding of a thesaurus is simply a book of synonyms, that is, alternatives to a core glossary when this is not rich enough to express a full range of the relationships. It is essential to rhetoric.

Any thesaurus makes strong ontology and ontological metaphor assumptions. That is, the list of words that are encouraged or allowed as substitutes will reflect a sometimes-subtle point of view. Though hardly as shaping as a defining vocabulary, the illusion of choice may play a role in getting people to accept authority. For instance:

political view

In English, Roget's original thesaurus has a strong influence on how people view the use of English itself. Roget's has been criticized for reinforcing various conceptual metaphors of colonialism and imperialism, for instance, by encouraging paternal metaphors for the state. An issue taken up later by George Lakoff in his Moral Politics.

poet/troll view

However, even a slight freedom of choice provides power in the case of language, so poets and other trolls can perhaps more easily exploit a thesaurus than any authority. George Orwell's newspeak was a fictional language devoid of words that could be used in a thesaurus: it steered thought so as to avoid unauthorized thought, or "thoughtcrime".

This idea of restricting words has been very influential in the theory of deep framing and in user interface design - for instance, all command verbs in a user interface have some capacity to evoke metaphors. The word "go" for instance implies spatial metaphor and likens a sequence of images or pages to a sequence of steps. A thesaurus would permit other words to be substituted so as to be less spatial, so if the spatial metaphor were useful to the power structure (for instance, to give people a sense of moving even as they sat still and generate health problems via obesity), it might be undesirable.


The US Government FEA Capabilities Manager project assumes:

"A thesaurus is a higher order form of semantic model than a taxonomy because its associations contain additional inherent meaning. In other words, a thesaurus is a taxonomy with some additional semantic relations in the form of a controlled vocabulary. The nodes in a thesaurus are "terms," meaning they are words or phrases. These terms have "narrower than" or "broader than" relationships to each other. A thesaurus also includes other semantic relationships between terms, such as synonyms."

ontologist view

"Taxonomies and thesauri are limited in their semantic expressiveness because they offer only a one-dimensional axis on which to define relationships. As such, they are typically used to create a classification system," such as a set of categories. However, "they fall flat when trying to represent multidimensional and/or varied conceptual domains. Concepts are the bearers of meaning as opposed to the agents of meaning. They are largely abstract and therefore more complex to model. Concepts and their relationships to other concepts, their properties, attributes, and the rules among them cannot be modeled using a taxonomy. Other more sophisticated forms of models, however, can represent these elements."

"A semantic model in which relationships (associations between items) are explicitly named and differentiated is called an ontology. (In Figure 7, both conceptual models and logical theories can be considered ontologies, the former a weaker ontology and the latter a stronger ontology. Because the relationships are specified, there is no longer a need for a strict structure that encompasses or defines the relationships. The model essentially becomes a network of connections with each connection having an association independent of any other connection."

A thesaurus is thus a kind of taxonomy since it relies on a "tree" rather than "graph" structure.