Defining Boundary Knowledge Without Ontology

Scientific frameworks routinely encounter boundaries that resist direct description, including singularities, horizons, undecidable regimes, and scale limits. In many cases, these boundaries are treated either as placeholders for future ontology or as regions requiring speculative explanation. This paper argues for a different approach: boundary regions may require precise definition without descriptive content. Within the Paton System, Tier-8 represents such a boundary. It is not a domain of entities or mechanisms, but a limiting condition inferred through breakdown behaviour, curvature budgets, and constraint saturation. This paper formalises Tier-8 as boundary knowledge rather than ontological territory, clarifying why definition at this level is necessary for responsible use while description is neither possible nor admissible. The result is a viability-first account of boundary reasoning that preserves continuity, prevents misuse, and establishes a principled stopping rule.