Chapter 3: The Judicial Reasoning Space

“The law is not a brooding omnipresence in the sky, but the articulate voice of some sovereign or quasi-sovereign that can be identified.” — Oliver Wendell Holmes Jr., Southern Pacific Co. v. Jensen (1917)


RUNNING EXAMPLE — JUDGE RIVERA’S DOCKET

Judge Rivera’s voting rights case has landed. A coalition of civil rights organizations challenges a state law that eliminates three days of early voting and requires a specific form of photo identification that, the plaintiffs allege, minority voters disproportionately lack. The state argues the law prevents fraud and streamlines election administration.

Rivera must analyze this case. But what does “analyze” mean, precisely? She will consider the constitutional text (Equal Protection Clause, Fifteenth Amendment), the statutory framework (Voting Rights Act), the factual record (statistical evidence of disparate impact), the procedural posture (preliminary injunction hearing), the relevant precedent (Shelby County, Brnovich, Crawford), the available remedies (injunction, declaratory relief), and the public interest (democratic participation, election integrity).

These are not random considerations. They are dimensions of a space — the space of legal states. Every case Rivera has ever decided occupies a point in this space, characterized by its position along each dimension. Her task is to locate the current case in this space, identify the nearest precedents, and navigate from the current legal state to the appropriate legal outcome.

This chapter constructs that space.


The Judicial Complex: Construction

Why a Simplicial Complex?

The space of legal states is fundamentally discrete. There are finitely many decided cases, finitely many statutes, and finitely many constitutional provisions. Legal states do not form a continuum — you cannot “continuously vary” a case from Brown v. Board of Education to Plessy v. Ferguson. Cases are discrete points, and the connections between them (citations, doctrinal relationships) are discrete edges.

The mathematical structure that captures discrete points with connections is a simplicial complex — a collection of vertices (points), edges (connections between pairs), triangles (connections among triples), and higher-dimensional simplices (connections among larger groups). A simplicial complex is a combinatorial object: it is defined by listing which subsets of vertices are connected, without any reference to a continuous ambient space.

But the legal simplicial complex has additional structure that a generic complex does not: it is directed (citations go from later cases to earlier cases, and authority flows from higher courts to lower courts) and weighted (some connections are stronger or cheaper to traverse than others). We therefore work with a directed weighted simplicial complex.

Formal Construction

Definition (Judicial Complex). The judicial complex \mathcal{K} is a directed weighted simplicial complex constructed as follows:

Vertices (0-simplices). Each decided case c_i is a vertex. The vertex carries an attribute vector \mathbf{v}(c_i) \in \mathbb{R}^8, whose components are scores along the eight legal dimensions, and metadata including the deciding court’s level \ell(c_i) \in \{\text{trial}, \text{appellate}, \text{supreme}\} and the decision date \tau(c_i).

Directed edges (1-simplices). A directed edge c_i \to c_j exists when case c_j cites case c_i (the later case relies on the earlier one). Directionality encodes two asymmetries:

  • Temporal precedence: \tau(c_i) < \tau(c_j), since a case cannot cite a future decision. The citation graph is a directed acyclic graph (DAG) with respect to time.

  • Hierarchical authority: \ell(c_i) \geq \ell(c_j) for binding precedent. A district court must follow a Supreme Court precedent (low traversal cost), but the Supreme Court is not bound by the district court (high or infinite cost in the reverse direction).

The edge carries an asymmetric weight w(c_i \to c_j) \geq 0. The asymmetry is essential: the cost of traveling from a binding precedent to the current case is low (the precedent controls), while the cost of traveling in the reverse direction — from a lower court case to a higher court case — is high or infinite (the lower court does not bind the higher court).

Higher simplices. A k-simplex [c_0, \ldots, c_k] exists when the cases form a doctrinal cluster — a set of mutually citing cases that collectively establish a legal doctrine. The simplex inherits a partial order from the temporal and hierarchical ordering of its vertices.

Why Directionality Is Essential

The directionality of the judicial complex is not a technical nicety. It encodes the two most fundamental asymmetries of legal reasoning:

Temporal asymmetry. A case decided in 2024 can cite a 1954 precedent, but not vice versa. The citation graph is a DAG with respect to time. This means that legal reasoning is inherently historical: the path from a precedent to the current case follows the arrow of time, and the legal significance of the path depends on the temporal order.

If we forgot the directions — if we treated the citation graph as undirected — we would lose this temporal structure. We would treat “the current case cites Brown” and “Brown cites the current case” as equivalent, which is absurd: Brown was decided in 1954 and cannot cite a 2024 case.

Hierarchical asymmetry. A district court must follow a Supreme Court precedent (binding authority, low traversal cost), but the Supreme Court is not bound by any district court (no binding authority in the reverse direction, high or infinite traversal cost). The weight of an edge depends on its direction: w(c_{\text{Supreme}} \to c_{\text{District}}) \neq w(c_{\text{District}} \to c_{\text{Supreme}}).

If we forgot the directions, we would treat “the Supreme Court binds the district court” and “the district court binds the Supreme Court” as equivalent, which is constitutionally impossible.

The judicial complex is therefore inherently directed. This is not a choice — it is a structural feature of legal reasoning itself.

The Judicial Complex Is a Concrete Object

Unlike the continuous manifolds of differential geometry, which are abstract mathematical constructions, the judicial complex \mathcal{K} is a concrete, constructible object:

  • Vertices come from case databases. In the United States, databases like Westlaw, LexisNexis, CourtListener, and the Caselaw Access Project contain every published federal and state court decision. Each decision is a vertex.

  • Directed edges come from citation networks. Every judicial opinion cites prior cases, and these citations are catalogued in the databases. The citation is inherently directed: case B cites case A, creating an edge A \to B.

  • Attribute vectors come from the NLP scoring procedure. Each case’s text is embedded using a language-agnostic model and scored on the eight dimensions by trained linear probes. The procedure is deterministic: the same case text always produces the same attribute vector.

  • Edge weights are computed from the attribute vectors, the regime boundary structure, and the hierarchical cost function. The computation is a finite arithmetic operation.

The judicial complex is therefore not a theoretical abstraction that might someday be built. It is a data structure that can be constructed today from existing resources. The theoretical framework tells us what to build; the existing infrastructure provides the materials.

Regime Boundaries

Regime Filtration

In the simplicial complex framework, regime boundaries appear naturally as a filtration — a nested sequence of subcomplexes, each corresponding to a distinct legal regime.

Definition (Regime Filtration). The judicial complex admits a filtration

\emptyset = \mathcal{K}_0 \subset \mathcal{K}_1 \subset \cdots \subset \mathcal{K}_m = \mathcal{K}

where each \mathcal{K}_\alpha is a subcomplex corresponding to a distinct legal regime. The inclusion \mathcal{K}_\alpha \hookrightarrow \mathcal{K}_{\alpha+1} introduces edges that cross a regime boundary:

  • Jurisdictional boundaries — edges between state-court and federal-court vertices.
  • Statutory thresholds — edges between vertices on opposite sides of a statutory trigger (e.g., the “meeting of the minds” that converts negotiation into contract).
  • Constitutional limits — edges between vertices inside and outside the domain of a fundamental right.
  • Precedential boundaries — edges between vertices inside and outside the factual scope of a controlling holding.

The boundary penalty \beta in the edge weight formula makes crossing these boundaries costly, modeling the sharp legal transitions that characterize regime shifts.

Persistent Homology

The filtration structure enables persistent homology analysis: by varying the boundary penalty \beta, we can identify which topological features of the legal landscape are robust (persist across a range of penalties) and which are artifacts of a particular threshold choice.

A topological feature that persists as \beta varies from 0 to a large value is a structural feature of the legal landscape — it reflects a genuine discontinuity in the law. A feature that appears only for a narrow range of \beta values is an artifact — it depends on the specific penalty chosen and may not correspond to a real legal boundary.

This distinction is legally important. Some regime boundaries are sharp and universally recognized (the statute of limitations is either expired or it is not). Others are fuzzy and contested (where exactly is the line between commercial speech and political speech?). Persistent homology provides a formal tool for measuring the sharpness of legal boundaries.


RUNNING EXAMPLE — REGIME BOUNDARIES IN THE VOTING RIGHTS CASE

Judge Rivera identifies three regime boundaries relevant to her case:

1. The constitutional boundary. The Equal Protection Clause creates a boundary between permissible and impermissible voting restrictions. A law that classifies by race faces strict scrutiny (extremely costly to justify); a law that does not classify by race but has disparate impact faces a lower standard (the Brnovich factors). Rivera’s first task is to determine which side of this boundary the challenged law occupies.

2. The statutory boundary. Section 2 of the VRA creates its own boundary: a law that “results in” the denial of equal voting opportunity is prohibited. This boundary is distinct from the constitutional boundary — a law can be constitutional (surviving rational basis review) but still violate Section 2 (resulting in disparate impact). The two boundaries create a filtration: \mathcal{K}_{\text{constitutional}} \subset \mathcal{K}_{\text{statutory}} \subset \mathcal{K}.

3. The procedural boundary. The preliminary injunction standard creates a boundary between cases where relief is warranted and cases where it is not. The four-factor test (likelihood of success, irreparable harm, balance of equities, public interest) defines a surface in the legal space: cases on one side get the injunction, cases on the other side do not.

Each boundary imposes a penalty \beta on edges that cross it. An argument that crosses the constitutional boundary — claiming, for instance, that a facially neutral law is actually a racial classification — incurs a heavy penalty because crossing that boundary requires establishing discriminatory intent, which is difficult to prove. An argument that stays within the statutory boundary (Section 2 disparate impact) avoids the constitutional crossing but faces the Brnovich factors.

Rivera’s analysis is, in geometric terms, a search for the least-costly path from the plaintiffs’ position to the desired remedy — the path that crosses the fewest regime boundaries and incurs the lowest total penalties.


From Complex to Continuum

The Approximation Theorem

In the limit of dense case law — when decided cases tile the space of legal configurations finely — the weighted simplicial complex \mathcal{K} approximates a continuous Riemannian manifold \mathcal{J} with metric g_{ij}. The edge weights w(c_i, c_j) converge to geodesic distances ds^2 = g_{ij} \, dx^i \, dx^j, and the simplicial homology H_n(\mathcal{K}; \mathbb{Z}) converges to the singular homology H_n(\mathcal{J}; \mathbb{Z}).

We use the continuous notation where it clarifies the theoretical structure (for stating Noether-type balance principles, for instance), but the computational framework is discrete throughout. The judicial complex is a finite object, and all computations on it are finite.

The continuum limit is useful as a theoretical tool, not as a computational method. It tells us that the concepts we borrow from differential geometry — curvature, geodesics, parallel transport, holonomy — have well-defined analogues in the discrete setting. The discrete complex is primary; the continuous manifold is its asymptotic approximation.

Why Not Start with a Manifold?

One might ask: why not define the legal space as a continuous manifold from the start, and treat decided cases as sample points on it? This is the approach taken by some machine learning models of legal reasoning, which embed cases in a continuous vector space and compute distances using standard metrics.

The answer is that continuity is a fiction in the legal domain. Legal states are discrete: there are finitely many decided cases, and each case is a distinct point. The transition between “liable” and “not liable” is a sharp boundary, not a continuous gradient. The hierarchical authority structure is a discrete lattice (trial < appellate < supreme), not a continuous ordering.

Starting with a simplicial complex respects the discrete nature of legal data. The continuum limit is then a theorem — a result that tells us when continuous methods provide good approximations — not an assumption that forces us to smooth over the sharp boundaries that are essential to legal reasoning.

Constructing the Attribute Vectors

Determinism and Reproducibility

A legally authoritative scoring system must be deterministic: the same case text must produce the same attribute vector every time. The pipeline achieves this through two design choices:

  1. Fixed embeddings. The embedding model is frozen at a specific version. Its weights are not updated during or after deployment. The same input text always produces the same embedding vector \mathbf{e}(t_i).

  2. Linear probes. Logistic regression is a deterministic function: given fixed weights \mathbf{w}_k and a fixed embedding \mathbf{e}, the score f_k(\mathbf{e}) = \sigma(\mathbf{w}_k^T \mathbf{e} + b_k) is uniquely determined. There is no sampling, temperature parameter, or non-deterministic decoding.

This contrasts sharply with LLM-based scoring, where the same prompt can produce different outputs across runs (due to sampling), across model versions (due to weight updates), and across providers (due to different fine-tuning). An LLM-scored attribute vector is a random variable; a probe-scored attribute vector is a fixed function of the input text. For a system whose outputs may inform legal decisions, this distinction is dispositive.

Validation: Preventing Probe Hallucination

A critical concern for any NLP-based scoring pipeline is probe hallucination: the risk that the linear probes assign confident but incorrect dimension scores. We address this through four mechanisms:

  1. Ground-truth calibration. A validation set of approximately 200 cases is scored by legal experts (law professors or experienced practitioners) on all eight dimensions. The probes’ F_1 scores against this ground truth provide the quality floor.

  2. Confidence thresholding. Scores near 0.5 (low confidence) are flagged as uncertain. Only cases where all eight probes exceed a confidence threshold |p_k - 0.5| > \delta are used for metric calibration.

  3. Consistency checks. Legal dimensions have known structural constraints: procedural posture (d_3) should be high in cases that turn on standing or jurisdiction; remedial scope (d_7) should correlate with the presence of damages language.

  4. Ablation. Remove each probe in turn and measure the effect on downstream tasks. Probes that contribute noise rather than signal are detected by ablation.

Chapter Summary

  1. Legal analysis operates in an eight-dimensional space, with each dimension corresponding to a fundamental category of legal analysis: entitlement structure, factual nexus, procedural posture, statutory authority, constitutional conformity, precedential constraint, remedial scope, and public interest.

  2. The judicial complex \mathcal{K} is a directed weighted simplicial complex whose vertices are decided cases, whose directed edges are citations, and whose attribute vectors encode positions along the eight legal dimensions.

  3. Directionality is essential: it encodes temporal asymmetry (cases cannot cite future decisions) and hierarchical asymmetry (higher courts bind lower courts, not vice versa).

  4. Regime boundaries — jurisdictional limits, statutory thresholds, constitutional boundaries — appear as a filtration of the complex. Crossing a boundary incurs a penalty, modeling the sharp transitions of legal regime changes.

  5. The complex is a concrete, constructible object: vertices come from case databases, edges from citation networks, and attribute vectors from an NLP scoring pipeline.

  6. In the dense-case limit, the complex approximates a continuous Riemannian manifold, connecting the discrete framework to the tools of differential geometry.


Worked Example: Constructing a Mini-Complex

Consider a simplified judicial complex containing five cases in the area of voter ID law:

Case Court Year d_1 d_2 d_3 d_4 d_5 d_6 d_7 d_8
c_1: Harper v. Virginia Supreme 1966 0.9 0.6 0.9 0.3 0.9 0.7 0.8 0.9
c_2: Crawford v. Marion County Supreme 2008 0.7 0.5 0.9 0.5 0.7 0.8 0.6 0.7
c_3: Shelby County v. Holder Supreme 2013 0.8 0.4 0.9 0.8 0.9 0.9 0.7 0.9
c_4: Brnovich v. DNC Supreme 2021 0.8 0.6 0.9 0.7 0.6 0.9 0.6 0.8
c_5: Rivera’s case District 2026 0.9 0.7 0.8 0.6 0.8 0.5 0.7 0.9

Citation edges (directed): - c_1 \to c_2 (Crawford cites Harper): hierarchical cost h = 0 (same level, Supreme to Supreme). - c_1 \to c_3 (Shelby County cites Harper): h = 0. - c_2 \to c_4 (Brnovich cites Crawford): h = 0. - c_3 \to c_4 (Brnovich cites Shelby County): h = 0. - c_2 \to c_5 (Rivera’s case cites Crawford): h = 0 (binding: Supreme Court to district court). - c_4 \to c_5 (Rivera’s case cites Brnovich): h = 0 (binding).

Edge weights. For the edge c_2 \to c_5 (Crawford to Rivera’s case): - Attribute-vector difference: \Delta \mathbf{v} = (0.2, 0.2, -0.1, 0.1, 0.1, -0.3, 0.1, 0.2) - Mahalanobis distance: \Delta \mathbf{v}^T \Sigma^{-1} \Delta \mathbf{v} (requires the covariance matrix) - Regime boundary: no boundary crossing (same area of law, same constitutional framework) - Hierarchical cost: h = 0 (binding precedent) - Total weight: the Mahalanobis distance plus any boundary penalties

For the edge c_4 \to c_5 (Brnovich to Rivera’s case): - \Delta \mathbf{v} = (0.1, 0.1, -0.1, -0.1, 0.2, -0.4, 0.1, 0.1) - The large negative component on d_6 (precedential constraint drops from 0.9 to 0.5) reflects that Rivera’s case is less constrained by precedent than Brnovich was. - Total weight: comparable to the Crawford edge, but the dimensional profile differs.

This mini-complex illustrates the basic structure: cases as vertices, citations as directed edges, attribute vectors as coordinates, and edge weights as costs of doctrinal traversal. The full judicial complex for voting rights law would contain thousands of cases and tens of thousands of edges, but the structure is the same.


Technical Appendix

Definition (Directed Weighted Simplicial Complex). A directed weighted simplicial complex is a tuple \mathcal{K} = (V, E, S, \mathbf{v}, w) where: - V is a finite set of vertices. - E \subset V \times V is a set of directed edges (ordered pairs). - S is a set of higher simplices, each a subset of V with a compatible partial order. - \mathbf{v}: V \to \mathbb{R}^n assigns an attribute vector to each vertex. - w: E \to \mathbb{R}_{\geq 0} assigns a non-negative weight to each directed edge. The weight function is asymmetric: w(u \to v) \neq w(v \to u) in general.

Definition (Regime Filtration). A regime filtration of \mathcal{K} is a sequence \emptyset = \mathcal{K}_0 \subset \mathcal{K}_1 \subset \cdots \subset \mathcal{K}_m = \mathcal{K} of subcomplexes such that the inclusion \mathcal{K}_\alpha \hookrightarrow \mathcal{K}_{\alpha+1} introduces edges crossing a regime boundary. The boundary penalty \beta_\alpha for crossing boundary \alpha is added to the edge weight.

Proposition (DAG Property). The citation subgraph of \mathcal{K}, restricted to edges encoding temporal citation (later case cites earlier case), is a directed acyclic graph (DAG). This follows from the impossibility of citing a future decision.

Proposition (Convergence to the Continuum). Let \mathcal{K}_N be a sequence of judicial complexes with N \to \infty vertices whose attribute vectors tile [0,1]^8 with mesh size \epsilon_N \to 0, and whose edge weights are given by the Mahalanobis formula. Then the metric space (V(\mathcal{K}_N), w) Gromov-Hausdorff converges to a Riemannian manifold (\mathcal{J}, g) where g_{ij} = (\Sigma^{-1})_{ij} is the inverse covariance metric.

Definition (Attribute Vector via NLP). Given case text t_i, the attribute vector is:

\mathbf{v}(c_i) = \bigl(\sigma(\mathbf{w}_1^T \mathbf{e}(t_i) + b_1), \; \ldots, \; \sigma(\mathbf{w}_8^T \mathbf{e}(t_i) + b_8)\bigr)

where \mathbf{e}(t_i) is the LaBSE embedding, \sigma is the sigmoid function, and (\mathbf{w}_k, b_k) are the trained probe parameters for dimension k.


Notes on Sources

The simplicial complex construction draws on Hatcher (2002) for algebraic topology, Edelsbrunner and Harer (2010) for persistent homology, and Grigor’yan, Lin, Muranov, and Yau (2012, 2014) for path homology on directed graphs. The eight legal dimensions are synthesized from Hart (1961), Posner (1990), and the Restatements of Law, cross-referenced with the nine moral dimensions of Bond (2026a, Geometric Ethics). The NLP calibration pipeline adapts the methodology of Bond (2026a), independently replicated by Thiele (2026). The voter ID case law includes Harper v. Virginia Board of Elections (1966), Crawford v. Marion County Election Board (2008), Shelby County v. Holder (2013), and Brnovich v. Democratic National Committee (2021). Hart’s core/penumbra distinction appears in The Concept of Law (1961). Sunstein’s incompletely theorized agreements appear in Legal Reasoning and Political Conflict (1996). Dworkin’s integrity thesis appears in Law’s Empire (1986).