The Chain Rule and Composite Change in Interacting Systems: How Calculus Tracks Cascading Effects
The chain rule explains how change moves through composite pathways in interacting systems. This article develops the chain rule as a formal theorem about composite functions and as a modeling tool for mediated change, nested mechanisms, pathway sensitivity, feedback, Jacobian composition, and automatic differentiation. It shows how emissions can affect concentration, forcing, temperature, and ecological stress; how policy can affect behavior, contact, transmission, and outcomes; and how computational graphs propagate gradients through intermediate values. The article emphasizes that a composite derivative is a product or composition of local sensitivities, not a black-box response. Companion workflows in Python, R, SQL, and Haskell include chain-rule pathway audits, composite sensitivity decompositions, finite-difference checks, typed pathway records, assumption registries, Jacobian notes, implementation warnings, and advanced mathematical audit reports for responsible interpretation of mediated system change across nonlinear, feedback-rich, policy-sensitive, and computationally implemented models.









