Classification is fundamental to science. For science trades in generalities — sometimes laws, sometimes exception-riddled rules of thumb — and our schemes of classification set the terms for this engagement with the world. Of course, there’s more that science does and classification is not typically an end in itself. But for the Scientific Realist, it is difficult to separate the historical success of science from improvement in the way scientists classify. If our classifications manage to get something right about the world, to what do they refer or correspond?

Many philosophers will say natural kinds. But traditional accounts of natural kinds have notoriously struggled to accommodate the vagaries of classificatory practice in the biological sciences. This most evident for the classification of species — where the thesis that species are natural kinds has fallen substantially out of favor — but problematic as well for less charismatic examples such as our classification of cells, tissues, diseases, ecosystems, and so on. Philosophers of biology have generally regarded Richard Boyd’s “Homeostatic Property Cluster” (HPC) account of natural kinds to feature the right balance of flexibility and specificity. I argue, however, that while an improvement on essentialist and metaphysics-first approaches to natural kinds, the HPC account faces conceptual problems and difficulties of application to cases even within its putative stronghold. 

One fruitful diagnosis of these problems begins with the observation that the HPC account shares with essentialism a "bottom-up" approach to natural kinds that makes their metaphysics more central and less flexible than scientific practice requires. My alternative account, by contrast, takes a more "top-down" orientation that starts from the epistemic role that such kinds play in science and deemphasizes the metaphysics underpinning this role. I conceive of natural kinds “adjectivally”: rather than seeing natural kinds as an ontological category, as a left-alone feature of reality, it is better to think of “natural kindness” as a status that a category can possess in virtue of its aptness to contribute to our explanatory and inferential practices. This status is domain- and context-relative, however, introducing a dose of pragmatism into an account of biological kinds.

The book uses a range of case studies of biological classification to motivate and articulate this account, addressing the resulting tension between realism and pragmatism.

Tentative Table of Contents

Chapter sketches and drafts to be posted here in due course.

1. Scientific Realism and the Essentialist Tension

2. Biomolecules

3. Cell Types

4. Natural Kinds from the Top Down

5. Tissues and Organs

6. Diseases

7. Race

8. Ecosystems

9. Envoi: Pragmatism for Realists