 The notion of a model is also used more widely outside structuralist interpretations of scientific theories. Talk of models often refers to fragments of theories, to mere approximations and to objects (or descriptions of objects) that are used to represent a given target. Given that the common interpretation of classical conceptions of reduction requires the relata to be fully fledged theories, it is not clear how sciences such as biology, psychology, and neuroscience fit into the picture. In these areas, such imperfect, highly idealized or merely approximately correct models dominate theorizing, and often model-descriptions are accompanied by visualizations, which might raise further questions as to the applicability of purely or mainly syntactic notions of reduction (Bechtel &amp; Abrahamsen 2005). There are no definitions of reduction that accommodate that fact directly; that is, there are no definitions of how one model reduces to another that might serve as a counterpart to those we have for theory-to-theory reduction. Rather, definitions of reduction directed at model-based theorizing are often described in ontological terms: It is the mechanisms, or phenomena captured by the models that allegedly reduce. The models themselves reduce only in a derivative sense (a discussion of these and related issues is covered in the entry on  reductionism in biology.)