A taxonomy of theory must reflect differences among the goals or objectives, the structure, and the foci of domains of different kinds of theories, and hence, their modes of understanding. As a result of differences in objectives, structure and domain, theories can be classified along at least the four axes of temporality, phenomenology, abstraction and generality (see Table 2). But, because theories are complex systems, a single theory can have components that span different classes. The four axes are not mutually exclusive.
Theoretical understandings differ in their emphasis on the degree and kinds of causality attributed to prior states vs. current relationships. The term `contingency' allows the understanding that current relationships and constraints have accumulated from past interactions.
Theories may conceptualize phenomena as being caused by dynamic interactions (phenomenology) which are not reducible to components at lower levels, or as being caused by underlying mechanisms. Hierarchical nesting usually allows us to ignore typical contradictions between these two extremes (Pattee 1973).
Models may range from highly specific space-time contexts to abstract, ideal (including unreal) systems.
Theories unlinked by nesting or hierarchy to other theory may maximize only two of the following three parameters: generality, precision, realism (Levins 1966). The degree of generality or specificity of a theory depends on the extent to which both precision and realism are being employed. If both are considered important, generality will be minimal.