Philosophy, Psychiatry, & Psychology 9.3 (2002) 219-227
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The Practical Kinds Model as a Pragmatist Theory of Classification
Pragmatist theories of scientific classification are intended to be pluralistic models that recognize different ways of cutting up the world as valuable, but do not require us to adopt whatever-goes relativism or metaphysical antirealism. How ironic that my application of pragmatism to psychopathology has been charged with not being sufficiently pluralistic because it tries to fit all psychiatric disorders into the Procrustean bed of practical kinds.
The Practical Kinds Model in General
As a point of clarification, the practical kinds model is not a description of a type of category combined with an argument that all psychiatric disorders should be seen as belonging to that type. If it were that kind of model, I would fully agree with Haslam that practical kinds, fuzzy kinds, and discrete kinds are all potential types of psychiatric disorders. Like Nick Haslam, I believe that there are many different things in the DSM-IV and the ICD-10, and they cannot neatly be classified as the same type of thing.
Rather than identifying a type of category, the practical kinds model is a general theory of scientific classification. It is a nonessentialistic theory. Essentialism is the view that things have real essences. In the Aristotelian version of essentialism, an essence is an internal structure, and it is the internal structure that makes anything be the kind of thing it really is. In this classical category model, category members either have the essence or they do not, and everything that has the appropriate essence is a member of that category. The world is supposed to therefore have a well-defined structure, and the job of the scientist is to discover that structure. Ian Hacking (1999) has termed this view of categorization inherent structurism.
The practical kinds model does not deny that things have internal structures; it only denies that internal structure by itself determines category membership. Internal structure is an important consideration in identifying categories, but external criteria can always play a role. External or relational criteria play more important roles in some cases than they do in others, but they cannot be eliminated once and for all. Essentialistic theories, which favor an almost exclusive focus on inherent structures, have the advantage of being more parsimonious, but they do so by ignoring real complexity.
The best way to illustrate this point is to examine a category whose identification is heavily weighted in terms of internal criteria, or an inherent structure, such as a chemical element. [End Page 219] For example, hydrogen is defined as the element that has an atomic number of 1. This means that it has one proton in its nucleus and normally one electron orbiting its nucleus. The atomic number reflects an internal property, and anything that has an atomic number of 1 is hydrogen. The same is true for the other elements. Anything that has an atomic number of 79 is gold; anything that has an atomic number of 19 is potassium, and so on. Also part of the essentialistic view is the notion that all the important properties of an element are systematically (or lawfully) related to its internal structure.
It would be foolish to deny the practical utility of the atomic theory of chemistry. But even in this strongest of cases, external criteria can potentially play a role in how we decide to carve up the world and what we identify as the relevant categories. The point can be clearly illustrated with a Gedanken experiment based on the ideas of Donnellan (1983). Assume that we were to make contact with extraterrestrial life, and the result of that contact was our initiation into a larger galactic community like those portrayed on Star Trek or Babylon 5. Fortunately for us, it turns out that all planets in the community use a gold-based currency, just like we do on Earth. What we call gold, however, is too common to be the galactic basis of a currency, but a particular isotope...