A Stylometric Analysis of Amadís de Gaula and Sergas de Esplandián (2022)

Abstract: Amadís de Gaula (AG) and its sequel Sergas de Esplandián (SE) are masterpieces of medieval Spanish chivalric romances. Much debate has been devoted to the role played by their purported author Garci Rodríguez de Montalvo. According to the prologue of AG, which consists of four books, the author allegedly revised the first three books that were in circulation at that time and added the fourth book and SE. However, the extent to which Montalvo edited the materials at hand to compose the extant works has yet to be explored extensively. To address this question, we applied stylometric techniques for the first time. Specifically, we investigated the stylistic differences (if any) between the first three books of AG and his own extensions. Literary style is represented as usage of parts-of-speech n-grams. We performed principal component analysis and k-means to demonstrate that Montalvo’s retouching on the first book was minimal, while revising the second and third books in such a way that they came to moderately resemble his authentic creation, that is, the fourth book and SE. Our findings empirically corroborate suppositions formulated from philological viewpoints.

## introduction amadís de gaula (ag), which is a medieval spanish chivalric romance published at the beginning of the sixteenth century, has long been considered a masterpiece of the genre. its sequel sergas de esplandián (se) came out a few years after. both works have been attributed to garci rodríguez de montalvo, a lower-class aristocrat from medina del campo in the present-day valladolid prefecture. note that no other work has been ascribed to him. ag consists of four books. together with its sequel se, there are a total of five books in the series, even though the latter was published separately. according to the prologue of ag, the author revised the first three books that were in circulation at that time, and translated the fourth book and se from a greek manuscript he had encountered. in reality, however, they are both considered his own creation; feigning a translation was a literary commonplace back then. still, the extent to which the author modified the materials at hand to compose the extant version has yet to be extensively explored. to delve into the enigmatic composition of montalvo's works, we applied stylometric analysis for the first time, to the best of our knowledge. stylometry is a field of study that, among other goals, aims to identify authorship of disputed or anonymous documents @xcite @xcite @xcite . specifically, we investigated the stylistic differences (if any) between the first three books of ag and his own extensions, that is, the fourth book of ag and se. literary style is represented as usage of parts-of-speech (pos) n-grams. since the employment of syntactic features is supposed to be fairly unconscious and hardly imitable, pos n-grams, which capture partial syntactic information, can reasonably serve as stylistic fingerprints. we performed principal component analysis (pca) and k-means to demonstrate that montalvo's retouching on the first book was minimal, while revising the second and third books in such a way that they came to moderately resemble his original contributions, that is, the fourth book and se. our findings empirically corroborate suppositions formulated from philological viewpoints by cacho blecua (rodríguez de montalvo, 2020a). the rest of the paper is organized as follows. in section 2, we review related research. section 3 describes the methodology utilized. in section 4, we present experimental results, followed by a discussion in section 5. section 6 concludes the study by discussing future research directions. ## related work research on the genesis of the amadisian oeuvre has been conducted by hispanic philologists including cacho blecua (rodríguez de montalvo, 2020a,b), domingo del campo (1982), and sainz de la maza (rodríguez de @xcite . however, few scholars have exhaustively inspected the linguistic usage therein. labrousse (2021) studied a variation of nominal phrases containing possessives in the first and fourth books of ag and found discrepancies between them. however, the second and third books of ag as well as se were not included in her scope of study. moreover, the analysis was restricted to the first 500 occurrences of the construction in question. to gain a more complete picture, a comprehensive scrutiny is needed. over the past few years, spanish philology has witnessed an increasing number of stylometric studies @xcite @xcite @xcite @xcite . the style markers used have been mostly limited to functional words and frequent words. pos ngrams have been rarely adopted even though its effectiveness has been confirmed by various studies addressing literary works in multiple languages including english @xcite @xcite @xcite @xcite , french @xcite , japanese (uesaka and murakami, 2015), and recently in spanish @xcite . the advantages of leveraging pos sequences are multi-fold: (i) their numerous occurrences provide reliable statistics; (ii) they are relatively independent from content; (iii) being out of conscious control of the author, they are supposed to be hardly imitable; and (iv) they partially capture syntactic patterns, which have been shown to be reliable style markers @xcite . ## methods the digitized texts of ag and se were retrieved from corpus of hispanic chivalric romances foot_0 . for ag, we used the version published in seville in 1539 by the printer juan cromberger foot_1 . for se, we employed the version published in rome in 1525 by the printers jacobo de junta and antonio de salamanca foot_2 . they were the only digitized texts available, although the first edition of ag goes back to 1508 and se back to 1510. ag consists of 133 chapters arranged across four books: ag1, ag2, ag3, and ag4. the token size amounts to 530,000 words. se is composed of 184 chapters forming a single book. the token size adds up to 190,000 words. since the chapter length varies considerably from one another, we decided to generate equal-length pieces of 10,000 words from respective books. the prologues and epistolary passages were omitted in advance. note that book division was maintained for the subsequent analyses, while chapter division was disregarded. as for the final part of a book, where the piece length was below 10,000, it was treated as an independent one if it exceeded 6,000 words; otherwise, it was merged into the penultimate piece. thus, ag1 resulted in 13 pieces, ag2 in 9, ag3 in 11, ag4 in 16, and se in 18. for stylistic features, we leveraged pos n-grams. the tags were assigned using a tagger designed for present-day spanish spacy 3.3.1 foot_3 . the model employed was es dep news trf, which is larger and more accurate. we utilized this tagger because there are no publicly available ones designed for medieval spanish, in which the amadisian works are written. based on the philological expertise, we modified extensively the texts prior to tagging to facilitate correct parsing; specifically, we applied as much orthographic modernization as possible. for instance, auer "to have" was transformed into its modern counterpart haber and certain words were separated, like acostose was separated into acostó se "he/she lay down". aux and propn were merged into verb and noun respectively as their correct identification proved to be hardly feasible. for frequent functional words including auxiliary verbs, adverbs, conjunctions, and prepositions, we adopted surface forms in lieu of the assigned tags to make the most of their differing usage, for example, the preposition de "of" was not converted into adp but maintained as such. as for verbs, we distinguished among infinite forms, that is, infinitives (inf), gerunds (gerund), and past participles (ppart) and gave them distinct labels. in contrast, the finite forms were uniformly given an identical label regardless of mode, tense, grammatical person, and number. in addition, we differentiated highly frequent verbs haber "to have" and ser "to be" by tagging the relevant forms with their infinitival forms. as for punctuation, we only retained periods and question marks representing sentence boundaries and omitted commas, colons, and semicolons that could stem from editorial interventions. these measures resulted in 54 tag types in total. tagging performance was evaluated by computing an accuracy rate on randomly chosen five hundredword passages: one from each of the four books of ag and another from se. the mean accuracy was almost perfect at 0.99 ± 0.01. note that, without manual modification of the texts and tags, the mean accuracy declined to 0.83 ± 0.02. every piece was represented as a vector whose elements represent z-transformed relative frequencies of the n-grams. we considered only the most frequent pos n-grams above a given rank threshold, while the remainder was aggregated under the label of others. to assess the robustness of our analyses, we varied the n-gram size n for @xmath0, 2, 3, 4} and the rank threshold r for @xmath1, 300, 500}. for @xmath2, r was fixed to 54, which was the number of unigram types. ## analysis for illustrative purposes, we present the results obtained with (n, r) = (3, 300). figure 1 displays the pair-wise distance scores between the pieces, computed as next, we conducted two types of exploratory multivariate analyses, pca and k-means, to examine whether any stylistic difference was found across the books. ## conclusions this study addressed a long-standing enigma concerning the genesis of the two monumental works authored by montalvo. applying stylometric techniques, we demonstrated that montalvo's retouching on ag1 was minimal, while revising ag2 and ag3 to such an extent that they came to moderately resemble his authentic creations, ag4 and se. our findings empirically corroborate suppositions formulated from philological viewpoints by cacho blecua (rodríguez de montalvo, 2020a). one limitation of our study is the lack of distinction between narration and conversation. the distinction is desirable, because varying proportions of the two components across the books could potentially affect the study's outcome. in so doing, we can also examine if authorial fingerprints are more clearly detectable in one part than in the other.