Relationship Types and Taxonomies

Most scientific fields depend on classification systems. Chemistry has its periodic table of elements, biology has its classification of species, and personality psychology has a model of fundamental traits. Each of these classifications is a scientific taxonomy: a systematic way of describing a field of knowledge. Taxonomies serve several important functions. First, they enumerate the varied phenomena that exist in a particular field. By comprehensively describing these variations (e.g., stating how many types of elementary particle exist), a taxonomy provides a map of its scientific territory. Second, taxonomies enable communication, supplying people with a shared terminology for exchanging information. Third, taxonomies often go beyond simply listing and naming things, and they say something about how those things relate to one another. A classification of mental disorders, for example, tells us which psychiatric conditions are closely associated with which other conditions, and how different conditions can be distinguished. This entry describes taxonomies that have been developed to describe, name, and organize the diversity of human relationships.

Taxonomies serve these descriptive, communicative, and organizing functions in varying ways. For instance, some propose a set of categories, whereas others propose a set of dimensions. A categorical taxonomy, such as the classification of chemical elements or biological species, includes a number of discrete types. Anything it classifies either falls into a particular type or it does not: An organism either is a dog or it is not, and a molecule [Page 1354]either does or does not contain hydrogen. A dimensional taxonomy, in contrast, does not sort things into types, but provides a set of continuous dimensions on which they can be located, just as we can find a location on a map using its coordinates. The most widely accepted personality taxonomy, for example, proposes that there are five factors along which people differ by degree.

Another important difference between taxonomies relates to categorical classifications. Some of these, like the taxonomy of biological species, classify each entity into a single type. A particular bird may be either a spotted owl or a barn owl, but cannot be both at the same time. Other taxonomies allow entities to be classified into multiple types. The periodic table, for example, allows us to determine the different elements that constitute a particular molecule (e.g., hydrogen, oxygen, and carbon). Categorical taxonomies can therefore either tell scholars the mutually exclusive types that things belong to or the building blocks that compose those things. We can refer to these types of taxonomy as “exclusive” and “elementary.” All of these distinctions between taxonomies may seem rather abstract at this point, but this entry shows how they help researchers understand attempts to classify relationships.