Anchoring the cluster: refining Pigliucci's family resemblance proposal via a dual constraint model of moderate scientific realism.

Massimo Pigliucci attempts to solve the species problem by integrating Wittgenstein's family resemblance into a scientific realist stance. He proposes that species are interest-independent natural clusters, yet he simultaneously concedes to the purpose-driven pluralism found in biological practice. We argue that this proposal leaves a central tension: it lacks a normative account to explain how an interest-independent ontology coexists with pluralistic practice. Although Pigliucci attempts to defend this realist commitment by appealing to the efficacy of scientific practice, we contend that his defense is problematic. Specifically, his defense exhibits three flaws: first, the inference from practical convergence to strong scientific realism is insufficient; second, it creates an explanatory tension regarding the coexistence of convergence and divergence; and third, it fails to rule out a more parsimonious institutional explanation. In response, we propose a practice-based moderate scientific realism. Decoupling reality from interest-independence, we formulate this realism as a dual constraint model: the reality of species is anchored in the world's causal constraints, while the objectivity of classification is maintained through the community's normative constraints. By substituting strong scientific realism with moderate scientific realism, this approach refines Pigliucci's family resemblance proposal, offering a coherent solution to the species problem that reconciles realist commitments with pluralistic practice.