Projection-Limited Coherence: A Structural Theory of Effective Description from Physics to Cognition

We present a general structural framework for effective description based on projection, admissibility, and finite coherence capacity. The framework is independent of any specific physical model and applies wherever local descriptions cannot be extended to a single globally consistent representation. We prove general results on irreversibility, selection, and loss of predictability that follow solely from projection-limited coherence, without invoking stochastic laws, optimization principles, or observer-dependent assumptions. We then show how this abstract structure is instantiated in diverse domains, including fundamental physics, biological systems, cognitive processes, and large-scale social organization. In each case, phenomena such as decision thresholds, irreversibility, hesitation, and regime change arise as consequences of admissibility limits rather than domain-specific mechanisms. Modal Triplet Theory is presented as one explicit realization of this general structure in fundamental physics. The work provides a unifying language for understanding why effective descriptions fail, fragment, or reorganize across scales.