A polysystemic and triadic epistemology of chemical theory structure and change, Полісистемна та тріадна епістемологія структури та змін хімічної теорії

<jats:p>This article argues that existing epistemological frameworks, including Kuhnian accounts of paradigms, reductionism, and structural realism, are inadequate for capturing the distinctive dynamics of chemical knowledge production because they neglect the functional interdependence of heterogeneous subsystems within chemical theories. These approaches tend to model theoretical change in terms of monolithic paradigm shifts, reductive explanatory closure, or the preservation of formal mathematical structures. Chemistry, however, exhibits a more intricate pattern: theories evolve through selective, context-dependent reorganisation driven by mismatches between coordinated subsystems and material reality. We develop a polysystemic model [12, 13, 14] that distinguishes sixteen functionally differentiated subsystems within mature scientific theories. Extending previous formulations, we clarify the ontic status of these subsystems as heuristic partitions—analytically useful distinctions not intended to correspond to real cognitive modules. The principal methodological contribution of this paper is to operationalise the concept of \textit{material response} by specifying explicit diagnostic criteria, including thresholds for failure, independence of methods, and robustness across molecular classes. These criteria make it possible to trace theoretical change at the level of subsystem coordination in an empirically testable manner. Through detailed analyses of Molecular Orbital Theory and Density Functional Theory, supplemented by examples from computational chemistry workflows, we show how material responses drive selective subsystem reorganisation. We address the risk of conceptual inflation by demonstrating that the sixteen-subsystem taxonomy can be reduced to eight core subsystems without significant loss of explanatory resolution, with the remaining eight treated as derivative. Finally, we situate the polysystemic model among contemporary alternatives, including model-based science, mechanistic philosophy, and robustness analysis. We conclude that any epistemological framework aiming to provide a fine-grained account of chemical knowledge must treat approximative and procedural elements as central rather than peripheral features of theoretical development.  </jats:p>