Dust Theory Vol. 3: Endogenous Construction of Causality: Hume's Problem Solution and Causal Unity Based on Gradient-Relational Ontology (Gradient Cosmos Research Series)

The nature of causal necessity and the solution to Hume’s problem stand as core millennial puzzles in the philosophy of science. Existing causal theories—whether process causality, interventionist causality, or counterfactual causality—all presuppose substances, time, and natural laws as a priori premises. They cannot derive causal relations endogenously from more fundamental relations, and thus have never fully responded to Hume’s fundamental skepticism about necessary connection. Based on the axiomatic framework of Gradient-Relational Ontology, taking pure gradient relations as the sole primitive, this paper strictly constructs causal relations satisfying three criteria—temporal priority, statistical correlation, and intervention invariance—through the endogenous evolutionary mechanism of path condensation and rule steady state, without presupposing causal powers, entities, or a priori rules. The study demonstrates that causal necessity is neither a logical truth nor a psychological habit, but structural necessity formed by the gradient network filtered through free energy minimization. The structural constraint exerted by rule states on deviant conduction constitutes the ontological substrate of "necessary connection." This paper further proves that the three major traditional theories of causality—process causality, interventionist causality, and counterfactual causality—are all special cases of endogenous causality under different boundary conditions, and can be fully unified within the path-rule duality framework. This study provides a relationalist ontological answer to Hume’s problem and constructs the first fully endogenous system of causal philosophy.