We sought to demonstrate the relationship between ontologies, Knowledge Organization Systems (KOSs) formed by hierarchically organized entities and named in order to reflect a certain domain of knowledge, and the concept theory (CT) proposed by Ingetraut Dahlberg, who seeks to understand how the concepts are formed, what types of concepts exist and how they relate. Based on the fact that the classes and instances that compose the ontologies can be treated as concepts and also considering that the CT is applied to other KOSs, such as thesauri, a qualitative bibliographical research was carried out in order to investigate how Dahlberg's theory can be applied to a broader understanding of these systems of organization. It was verified that ontologies - taking into account all the elements that compose them (classes, instances, properties and facets) - may be understood through theoretical framework of CT, such as the formation of concepts and the different relationships that can be established among these. To demonstrate how this occurs, a simplified ontology was developed and each of the elements of its structure were discussed from the CT approach. It was concluded, in the end, that the approach of the ontologies through CT could provide a more efficient construction of these systems, since it allows a greater understanding of the domain to be described. However, it is important to emphasize that, although this approach provides greater completeness to the domains described in the ontologies, it is necessary to clearify that each ontology has a specific motivation for its development, that will limit how complete the definitions of the concepts can be. Therefore, even though the CT approach to ontologies may provide greater completeness, it is not always desirable, so it is necessary to take into account the purpose of the ontology and how it will be used
