Applying Information-theoretic Notions to Measure Effects of the Plain E nglish Movement on E nglish Law Reports and Scientific Articles (2024)

Abstract: We investigate the impact of the Plain English Movement (PEM) on the complexity of legal language in UK law reports from the 1950s-2010s, contrasting it with the evolution of scientific language. The PEM, emerging in the late 20th century, advocated for clear and understandable legal language. We define complexity through the concept of surprisal - an information-theoretic measure correlating with cognitive processing difficulty. Our research contrasts surprisal with traditional readability measures, which often overlook content. We hypothesize that, if the PEM has influenced legal language, there would be a reduction in complexity over time and a shift from a nominal to a more verbal style. We analyze text complexity and lexico-grammatical changes in line with PEM recommendations. Results indicate minimal impact of the PEM on both legal and scientific domains. This finding suggests future research should consider processing effort when advocating for linguistic norms to enhance accessibility.

## introduction legal language has been notorious for its intricate syntax and specialized jargon, making it challenging for non-experts to comprehend. this complexity has not only been a barrier to understanding for the general public but has also posed significant challenges for computational analysis. in response to this, the plain english movement (pem) emerged as a pivotal initiative in the latter half of the 20th century, advocating for clear, concise, and understandable legal language (cf. @xcite ). our study is corpus-based and explores whether this movement has led to a measurable change in the complexity of legal language, specifically uk law reports, from the 1950s to the 2010s. we contrast this with scientific language, which we hypothesize has not been similarly influenced by the pem. by comparing the evolution of language in these two domains, we work towards uncovering the unique trajectories of language complexity in response to professional and societal pressures. we define complexity based on the concept of surprisal -an information-theoretic measure of unpredictability in language, which has shown to be proportional to cognitive effort and thus processing difficulty @xcite . thus, high surprisal in a text, indicative of less predictable content, is associated with increased cognitive processing effort and serves as a reliable indicator of increased language complexity @xcite . we contrast surprisal with readability measures usually used to measure language complexity but often criticized for not taking into account the content of the text being evaluated (cf. @xcite ; @xcite ). in fact, while recently, in the computational linguistic community text simplification systems have been applied to simplify legal language @xcite , many open questions remain, for example, which information should be retained. here, a measure of informativity could enhance approaches on the matter. we introduce the pem and work on the diachronic tendency of phrasal compression as a densification strategy in specialized discourse, which is an opposite trend to what the pem advocates. we present our rationale putting forward two main hypotheses regarding law reports: if the pem has an impact, then we assume (h1) reduced complexity over time and (h2) change from a heavy nominal towards a verbal involved style. for scientific articles, we hypothesize no pem impact. we then present the corpora used and the methodology applied to measure text complexity and to analyze lexico-grammatical changes related to the suggestions of the pem. finally, our result section dives into a macro-analytical diachronic perspective and a micro-analysis of the linguistic features typical of contemporary law reports and scientific texts. results show that the pem had little to no impact on language use in these two domains. from this, we derive implications for future research that should account for processing effort when implementing linguistic norms towards increased accessibility. ## results and analysis considering the suggestions put forward by the pem, first, we test whether the overall text complexity is reduced especially for law reports (h1). second, an in-depth analysis of lexico-grammatical features will show whether the heavy nominal style changes towards a more involved verbal style (h2). ## conclusion we investigated the impact of the plain english movement (pem) on the complexity of legal language in uk law reports from the 1950s to the 2010s, contrasting this with the evolution of scientific language. the study was grounded in the hy-pothesis that if the pem had a significant influence, we should see a reduction in language complexity (h1) and a shift from a nominal to a more verbal style (h2) in legal texts. conversely, we anticipated that scientific language, not being a direct target of the pem, would not demonstrate similar changes. our findings, however, reveal that the impact of the pem on the complexity of legal language has been minimal. despite the efforts of the pem, legal language has largely maintained its traditional complexity and style. this suggests that professional norms and the inherent nature of legal discourse may resist simplification efforts, even in the face of concerted campaigns like the pem. surprisal and more elaborated notions of it ( cf. futrell (2023) ) can serve as a robust indicator of the cognitive load imposed on readers, thereby guiding the development of more accessible yet accurate renditions of complex information, often not captured by readability measures. we have employed it to quantify complexity to account for the unpredictability and processing effort associated with language comprehension. however, its application would not only enhance readability but also ensure that critical nuances and technical accuracies are not lost in the process of simplification. for example, endeavors to produce simpler legal texts (cf. @xcite ) would profit from using approaches which reflect processing effort and measure its reduction. the approach is general in nature and can be applied across various fields.