Legal- CGEL : Analyzing Legal Text in the CGELB ank Framework (2025)

Abstract: We introduce Legal-CGEL, an ongoing treebanking project focused on syntactic analysis of legal English text in the CGELBank framework (Reynolds et al., 2022), with an initial focus on US statutory law. When it comes to treebanking for legal English, we argue that there are unique advantages to employing CGELBank, a formalism that extends a comprehensive—and authoritative—formal description of English syntax (the Cambridge Grammar of the English Language ; Huddleston & Pullum, 2002). We discuss some analytical challenges that have arisen in extending CGELBank to the legal domain. We conclude with a summary of immediate and longer-term project goals.

## introduction there is widespread interest in the syntactic structure of legal language across multiple disciplines. for example, recent work in cognitive science has investigated how legal english differs from non-legal registers with respect to various syntactic features associated with processing difficulties @xcite . modern ai research assesses the ability of artificial systems to perform legal reasoning @xcite , which requires sophisticated understanding of complex syntactic structures found in legal documents. there is also significant interest within legal academia and the practicing legal community: legal outcomes can hinge on a judge's reading of a single structurally ambiguous phrase in a statute or contract. modern us legal theory (particularly the widely-adopted textualist framework of legal interpretation) relies on heuristics ('canons') designed to facilitate interpretation in 'hard' legal cases. for example, the conjunctive/disjunctive (cd) canon @xcite , revisited in §4.1) guides interpretation of negative disjunction of the form not a or b. according to this canon, "'not a, b, or c' means 'not a, not b, and not c'." linguistsincluding two co-authors of this paper-have at times weighed in directly through amicus curiae ('friend of the court') legal briefs on hard cases of textual interpretation, lending analytical insights into the syntactic as well as semantic properties of contested legal language @xcite . despite this interest, there exist (to our knowledge) no sizeable gold treebanks of legal english, limiting the ability of linguists to provide grounded, quantitative insights into the grammatical properties of legal language. we aim to rectify this empirical gap with legal-cgel, foot_0 an ongoing treebanking project focused on syntactic analysis of legal english text in the cgelbank framework @xcite . section 2 briefly recaps key properties of cgelbank, including design features which make cgelbank particularly wellsuited for legal english treebanking. section 3 describes legal-cgel's development procedure and presents key statistics of the treebank in its current in-progress form. section 4 demonstrates how legal-cgel enables empirical evaluation of the legal 'canons' of textual interpretation. section 5 concludes with future goals. ## why extend cgelbank to legal while cgelbank is a relative newcomer in the space of treebanking frameworks, it possesses advantages over more established formalisms such as penn treebank (ptb; @xcite and universal dependencies (ud; de @xcite when it comes to syntactic analysis of english in general and of legal english in particular. first, the grammar upon which it builds (the cambridge grammar of the english language, or cgel; @xcite aims to be an exhaustive account of english syntax: across more than 1700 pages, @xcite ground their analysis in many hundreds of distinct synthetic data points, resulting in "the most recent comprehensive reference grammar of english, describing nearly every syntactic facet of present day standard english" @xcite . cgelbank draws on cgel to provide a robust description of both english constituent structure (unlike ud) and grammatical functions (unlike ptb). its expressivity comes at the expense of cross-linguistic generalizability, which is important to other treebanking enterprises (e.g., ud) but is far less important in the context of us law. this analytical foundation is further augmented by the ongoing efforts of the cgelbank project, which evaluates and refines cgel against naturally-occurring corpus data: cgelbank 1.0 foot_1 analyzes 257 sentences from twitter and the english web treebank. moreover, cgelbank is uniquely interoperable across relevant academic disciplines and the professional legal community. this is because cgel is an authoritative formal description of english syntax familiar to lawyers and linguists alike. in the legal database westlaw, a search of the exact string "cambridge grammar of the english language" returns over 40 us state and federal cases in which the grammar is cited in a court opinion or order. this alone sets cgelbank far apart from ptb and ud, which invoke constructs that are likely unfamiliar to non-linguists in general and to the legal community in particular. for example, unlike cgelbank, "ptb... draws heavily from particular syntactic theories like government and binding" @xcite . by comparision, the core concepts of cgel are couched in widely-familiar descriptive terminology and are further explicated in an undergraduate textbook (a student's introduction to english grammar, @xcite , broadening the accessibility of cgel (and therefore cgelbank) to a more general lay audience. ## legal-cgel: current status the first iteration of legal-cgel focuses on us statutes, though the project may in principle be extended to other legal domains (e.g., contracts) and national contexts. to date, legal-cgel consists of 49 carefully-adjudicated trees of sentences drawn from the united states code, the official codification of us federal statutes as compiled by the office of the law revision counsel (olrc) of the united states house of representatives. we sourced sentences of legal-cgel from the olrc release point of the us code known as public law 118-78, foot_2 which reflects the state of the us code as of july 30, 2024. this release point is divided into 54 titles (e.g., title 17: agriculture) organized into chapters (e.g., title 17, ch. 24: honeybees) which are further subdivided into sections (e.g., title 17, ch. 24, §281: honeybee importation). the olrc maintains an xml-format digital version of the us code, structured using the united states legislative markup (uslm) standard maintained by the government publishing office. 4 within the treebank, every sentence is assigned a unique identifier based on the uslm metadata of its enclosing element. to simplify navigation and cross-referencing, we added a brief, distinctive prefix to each sentence id, e.g., usc-039 for the 39th sentence. we restrict our analysis to the primary statutory text of the us code; we ignore, e.g., statutory and editorial notes (which are associated with specialized uslm elements). the 49 sentences annotated to date were hand selected to highlight a diverse set of grammatical phenomena across a range of us code titles. the treebank currently consists of a total of 1675 lexical nodes (non-punctuation tokens) and an average of pos phrasal cat. gram. function 479 n 618 nom 2410 head 277 d 445 np 340 mod 276 p 341 vp 314 obj 153 v 290 pp 281 comp 120 adj 279 dp 276 det 96 v aux 235 clause 121 coordinate 55 coordinator 126 adjp 95 marker 40 sdr 55 coordination 83 subj 37 adv 41 clause rel 26 supplement 24 n pro 39 advp 24 predcomp 34 gap 14 prenucleus figure 2: counts for legal-cgel pos tags, phrasal categories, and grammatical functions. low-frequency category and function tags are omitted from the table. # sent _ @xmath0... # @xmath1:det (dp :head (d :t "the")) :head (nom :head (n :t "attorney") :mod (adjp :head (adj :t "general")))) figure 3: example of the project-native .cgel data format, demonstrating cgelbank analysis of the noun phrase the attorney general. 34.2 lexical nodes per tree. a breakdown of our data by cgelbank labels (pos, phrasal category, grammatical function) is presented in annotations are contributed by a team of five annotators (all co-authors of the paper), including one co-developer of the cgelbank framework (ns). the remaining annotators are students and scholars of linguistics trained in cgelbank analysis. initially, we reviewed annotations through live, teamwide discussions; however, more recent contributions were made using a github-based annotation procedure @xcite : annota-"upon failure to store or deliver to the secretary the farm marketing excess within such time as may be determined under regulations prescribed by the secretary, the penalty computed as aforesaid shall be paid by the producer." tors contribute trees directly to the project github repository as pull requests that are reviewed by the first and/or last author prior to acceptance. as part of this procedure, annotations are automatically visualized and validated using github action scripts. the automated cgelbank validator we employ has been shown to improve inter-annotator consistency @xcite . because adjudication proceeds over github, the project repository also contains numerous discussions between project contributors. these discussions, recorded as pull request comments, can help future researchers understand the rationale behind the analytical decisions reflected in the final annotations. sentences of the us code have posed analytical challenges not encountered in previous cgelbank annotation initiatives. for example, the project maintains a running list of legal terms of art (e.g., adversary proceeding, due process rights, attorney general) which are to be treated as single constituents. however, some analytical decisions are suggestive of revisions to the general cgelbank annotation guidelines @xcite . for example, cgelbank "as a rule, avoids invisibilia-but unbounded dependencies and other noncanonical word order constructions are the exception" @xcite . accordingly, for transitive vp coordinations, cgelbank treats the object as an np complement of a coordination phrase (as in figure 1 ) rather than marking the internal argument structure of the coordinated vps with gaps coindexed to the np. a challenge is posed by phrases such as the one found in figure 4 . for oblique dative constructions, cgelbank canonically marks rightward displacement of the direct object with a gap (e.g., deliver _ x to the secretary [the farm marketing excess] x ). when such constructions are coordinated with simple transitive vps (e.g., store... the farm marketing excess) to yield 'asymmetric' coordination structures, we made the decision to include gaps in both vps in order to maintain consistent co-indexing across both coordinated structures and to properly represent the fact that the single displaced np functions as the direct object of both verbs despite their different complement structures. ## testing canons of interpretation in this section, we show how legal-cgel can provide an empirical basis on which to evaluate the textualist 'canons' of legal interpretation. in two case studies, we show that some canons encode linguistic generalizations which are readily evaluated with the help of the cgelbank framework. our ultimate aim is to build automated parsers of us law, to obtain quantitative estimates of how well the canons describe actual conventions of legal drafting. for now, we focus on individual trees from our gold treebank to illustrate the potential of cgelbank in two distinct use cases. in section 4.1, cgelbank enables us to robustly characterize a class of sentences in which we expect to observe a legally-relevant semantic scope ambiguity. in section 4.2, cgelbank provides a formal characterization of a second relevant structural ambiguity, one for which the formalism additionally expresses the range of possible disambiguations. ## conclusion and future directions we have introduced and motivated legal-cgel, an ongoing legal treebanking initiative in the cgel-bank framework. in addition to expanding the tree-bank to many more sentences, we plan to measure inter-annotator agreement to assess the consistency of our annotation conventions. longer-term, we plan to build and evaluate automated cgelbank parsers, which will enable large-scale analysis of the syntactic properties of our target domain.