I. What This Work Is This monograph draws a line. Not to fence anything off, and not to declare any territory forbidden — but because without a line clearly drawn, too many arguments proceed as though the territory on both sides of it is the same kind of place, subject to the same rules, answerable to the same methods. It is not. The line exists whether or not it is acknowledged. This work is an attempt to make it visible. The line in question falls between two kinds of concepts. On one side are concepts that belong to science: testable, revisable, eliminable from a theoretical framework without changing the framework's structural character. Electrons, genes, neural correlates, entropy gradients — concepts whose presence or absence in a theory is a matter for experiment to settle. On the other side are concepts that belong to what this work calls meta-nature: structurally non-eliminable, resistant to testing not because we lack the right instruments but because the kind of thing they are makes the ordinary procedures of empirical confirmation structurally inapplicable. Existence, consciousness, normativity, the direction of time — concepts whose elimination from a framework does not simplify it but transforms it into a framework that can no longer ask the questions it was built to address. The argument for where the line falls is formal. It is grounded in the structural properties of ontological models — in what it means for a concept to be eliminable from a theoretical framework, and in what it means for an observational space to be evidentially connected to another. The result is a theorem: no concept can simultaneously be strongly falsifiable and structurally non-eliminable. The cell of the classification that would be occupied by such a concept is empty. This is not an empirical finding and not a matter of philosophical opinion; it follows from the structure of how concepts relate to the frameworks that represent them. But the theorem is not the point. The point is the map that surrounds it, and the diagnostic tool that the map makes possible. The theorem tells us that the line exists and where it runs. The map tells us what it looks like on both sides. The diagnostic tool tells us how to recognise, in the middle of a real argument, that the line has just been crossed. II. Who This Work Is For This work is addressed to three audiences, and it is designed to be useful to each without requiring the others. The first audience is philosophers working on ontology, philosophy of science, and the metaphysics of mind and normativity. For this audience, the formal apparatus is the main contribution: the two-axis classification, the Asymmetry Criterion, the X-sensitive evidential functor, the Bridge Principle Transmission Theorem, and the explicit statement of the four ontological commitments on which the framework rests. These are developed in Parts I and II and their technical foundations are in the Appendix. The second audience is scientists — particularly those working in neuroscience, physics, evolutionary biology, and AI research — who regularly encounter, produce, or evaluate arguments that cross the line between empirical and meta-empirical territory. For this audience, the diagnostic guide in Chapter 2 is the main contribution. It requires no prior knowledge of the formal apparatus. It is a practical tool for identifying, in the arguments of a research programme, the structural signs that the boundary has been crossed: the untested bridge principle, the elimination that changes the question, the positive results that do not satisfy. The third audience is anyone thinking seriously about what science can and cannot do — not out of scepticism toward science, but out of a desire to understand it precisely. Science is the most powerful tool we have for answering questions about the natural world. Understanding what kind of tool it is — what it is structurally capable of, and where its structural limits lie — is not a diminishment of science. It is an accurate description of something remarkable.