Every step has pointed at the same thing: a structure (Temporality, Spatiality, and Physicality together) that cannot fail to exist. That structure is what the book means by Nature. So at the level of necessity, Reality and Nature are the same thing, with no neutral ground outside the Conditions from which things could have been otherwise. One rival is still left standing, something transcendent alongside Nature, and that is taken up in Chapters 5 and 6.

Each step contributes one piece: the global modal status of possibility is fixed ([§2.1](<2.1 The S5 Pipeline.md>)); change is possible ([§2.2](<2.2 Cartesian Certainty.md>)); its possibility is necessary ([§2.3](<2.3 Necessary Possibility of Change.md>)); that necessity requires Temporality, Spatiality, and Physicality (§[§2.4](<2.4 Structural Requirement.md>)–2.5); the three are one change-realizing structure ([§2.6](<2.6 Triconditionality of Nature.md>)); and there is no empty alternative beneath it ([§2.7](<2.7 Nothing to Consider.md>)). Read together, they do not merely constrain what Reality could be: they identify its necessary structural content.

One identity bridge remains. Necessary co-instantiation alone would permit the thought that Reality has Nature as an endowment while remaining something more. Maximality and the available grounding positions close that remainder.

> [!argument]
> **The Reality–Nature Identity** · *The Grounding Trilemma*
>
> 1. Reality is the whole within which any real content belongs ([§1.1](<1.1 Reality.md>)).
>
> 1. Every real state, item, or world either instantiates the Conditions ([§2.6.8](<2.6.8 Ontological Identity.md>)) or is an abstraction of their structural features ([§2.6.12](<2.6.12 Necessity's Nature.md>)); either way it is conditioned by the necessarily instantiated structure ([§2.5](<2.5 Triconditional Necessity.md>)). Anything real is therefore a configuration within Nature or an abstraction from it, not an item standing outside its conditions of reality.
>
> 1. Let G be a proposed additional ground of Nature. G must either ground Nature, be grounded by Nature, or stand in no grounding relation to Nature ([§1.5.5](<1.5.5 Ground and Dependence.md>)).
>
> 1. If G grounds Nature, the grounding relation is directed, differentiates ground from grounded, and obtains as a real dependence. At role-resolution it reinstantiates T, S, and Φ; the alleged outside ground is already within the structure it grounds ([§2.2.2](<2.2.2 Actuality's Reach.md>), generalized at [§2.8.6](<2.8.6 Exclusivity of Nature.md>)).
>
> 1. If G is grounded by Nature, G is derivative within Nature. If G stands in no grounding relation to Nature, it is not an additional ground of Nature.
>
> 1. Therefore no real content or grounding office remains outside Nature. Structurally, Reality and Nature coincide: R = N.

The result closes the modal-structural identity needed here: everything real is conditioned by Nature, and no additional ground occupies an exterior grounding position.

The whole line, from the chapter's first move to its last:

> [!argument]
> **Necessity of Nature** · *The Whole Line*
>
> 1. *Necessary Possibility (T1).* Real possibility ranges over one fixed domain W, so whatever is possible is necessarily possible. ◇P → □◇P. ([§2.1](<2.1 The S5 Pipeline.md>))
>
> 1. *Cartesian Certainty.* The act of doubt is itself a change, so change is actual and therefore possible. ◇C. ([§2.2](<2.2 Cartesian Certainty.md>))
>
> 1. *Necessary Possibility of Change (L3).* T1 applied to the Cartesian witness yields □◇C. ([§2.3](<2.3 Necessary Possibility of Change.md>))
>
> 1. *Structural Requirement.* Necessarily possible change requires the three Conditions. □(◇C → (T∧S∧Φ)). ([§2.4](<2.4 Structural Requirement.md>))
>
> 1. *Triconditional Necessity.* The three Conditions are jointly and necessarily instantiated. □(T∧S∧Φ). ([§2.5](<2.5 Triconditional Necessity.md>))
>
> 1. *Triconditional Identity (T5).* Within change-realizing structure, the three Conditions form one mutually implicating realizer complex, with Nature naming their co-instantiation. ([§2.6](<2.6 Triconditionality of Nature.md>))
>
> 1. *Nothing Beneath.* No empty alternative lies under that structure. ¬◇∅. ([§2.7](<2.7 Nothing to Consider.md>))
>
> 1. *Reality–Nature Identity.* Reality is maximal, every real content is conditioned by Nature, and the Grounding Trilemma leaves no exterior grounding position. Structurally, R = N.
>
> 1. **Necessity of Nature (T6).** Therefore any possible Reality is Nature: the necessary co-instantiation of T, S, and Φ, with contingent configurations within it.

Six results unfold that identification, each inheriting the chapter-level closure: the structural laws are constitutive rather than contingent ([§2.8.1](<2.8.1 Laws as Constitutive.md>)), the denial of Nature is self-refuting ([§2.8.2](<2.8.2 Nature Cannot Be Denied.md>)), Φ presupposes T and S so the result is not physicalism ([§2.8.3](<2.8.3 Not Physicalism.md>)), contingency belongs to configurations within Nature rather than to Nature itself ([§2.8.4](<2.8.4 Necessity Precedes Contingency.md>)), Nature's necessity is formally stated ([§2.8.5](<2.8.5 Necessity of Nature.md>)), and every rival structural ground is precluded ([§2.8.6](<2.8.6 Exclusivity of Nature.md>)).

This is not one worldview set beside others to be weighed. It is the terminus of a derivation. T, S, and Φ are not predictions about what fundamental physics will eventually discover but role-level conditions any physics must already presuppose. Their realization as particular temporal metrics, spatial geometries, fields, laws, and material systems remains contingent physical content.

*Scope of the verdict.* The identity reached here is modal and structural: necessarily, any Reality instantiates Nature, and no additional ground occupies a position outside the Conditions. What this chapter does not yet close is the further claim that nothing transcendent stands alongside Nature under every theistic description. The structural form of that preclusion is set out at [§2.8.6](<2.8.6 Exclusivity of Nature.md>); its full form is the work of Chapters 5 and 6, and the unconditional verdict that Reality is Nature and nothing besides is not pronounced until Chapter 7, [§7.9](<7.9 Synthesis.md>).[^2-8-0-necessity-of-nature-ch4]

[^2-8-0-necessity-of-nature-ch4]: The Necessity of Nature is challenged across Chapter 4 by idealism ([§4.3.5](<4.3.5 Idealism.md>)), the Mathematical Universe Hypothesis ([§4.3.7](<4.3.7 Mathematical Universe Hypothesis.md>)), structural realism ([§4.3.9](<4.3.9 Structural Realism.md>)), Humean contingency ([§4.1.4](<4.1.4 Humean Contingency.md>)), and two-dimensional semantics ([§4.1.2](<4.1.2 Two-Dimensional Semantics.md>)). The Conceivability Trap ([§3.3.4](<3. Convergence.md>)) develops a convergent line, and phenomenal-consciousness objections are carried in Chapter 8.


- [2.8.1 Laws as Constitutive](<2.8.1 Laws as Constitutive.md>)
- [2.8.2 Nature Cannot Be Denied](<2.8.2 Nature Cannot Be Denied.md>)
- [2.8.3 Not Physicalism](<2.8.3 Not Physicalism.md>)
- [2.8.4 Necessity Precedes Contingency](<2.8.4 Necessity Precedes Contingency.md>)
- [2.8.5 Necessity of Nature](<2.8.5 Necessity of Nature.md>)
- [2.8.6 Exclusivity of Nature](<2.8.6 Exclusivity of Nature.md>)


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← [2.7.4 Preclusion Boundary](<2.7.4 Preclusion Boundary.md>) | [2.8.1 Laws as Constitutive](<2.8.1 Laws as Constitutive.md>) →
