Human beings tend to manage the complexity by breaking up experiences into manageable components that have meaning. These components are stored as mental representations, or concepts, that permit thinking when the object is not present. A fundamental part of learning concerns concepts, categories, and classification systems. To know that both of these fall into the taxonomic category of animals is even higher level classification and to know that angry dogs bite involves accessing a network of concepts. Recognition occurs when what is observed is placed into previously learned classes, or categories, on the basis of observed characteristics.
Human beings think of ideas as related to each other and the world as a somewhat orderly place.
The relationship among concepts is the basis for a hierarchical classification system and the organization of knowledge in a discipline. Science develops formal concepts to classify animals, plants, chemicals, minerals, and other things of scientific interest. In a science when concepts are considered important they become formal, standardized classifications within a system. For example, classifying a person as a citizen of the United States is important for determining rights and responsibilities. In the last half of the 20th century, nursing has recognized the importance of its clinical science and has constructed concepts, theories, and classification systems to further scientific development and patient care.