Revisiting Authorship Attribution of Tirant lo Blanc Using Parts of Speech n-grams (2023)

Abstract: Tirant lo Blanc (TLB) is a masterpiece of medieval Catalan chivalric romance. Regarding its authorship, two hypotheses exist: the single-authorship hypothesis claims in agreement with the dedication that Joanot Martorell is the sole author, whereas the dual-authorship hypothesis alleges in line with the colophon that Martorell wrote the first three parts and Martí Joan de Galba added the fourth part. In this study, we revisit the unsettled authorship attribution of TLB with stylometric techniques; specifically, we exploit parts-of-speech (POS) n-grams as stylistic features to investigate stylistic differences (if any) across the work. Furthermore, we address the distinction between narration and conversation, which has previously been omitted. We performed exploratory multivariate analyses and demonstrated that, despite internal differences, single-authorship is more likely from a statistical point of view. If Galba had contributed something to the last quarter of the work, it would have been minimal.

## introduction tirant lo blanc, hereafter tlb, is a chivalry novel written in catalan toward the end of the 15th century. its first edition was printed in 1490 in valencia, spain, although it had been supposedly composed between 1460 and 1465 @xcite . the medieval catalan literary masterpiece was praised for its style as "the best book in the world" by the 17th-century spanish writer cervantes in chapter vi of don quijote de la @xcite . the work was deemed to be the very first modern novel in europe by peruvian nobel laureate mario vargas llosa, who rediscovered and acknowledged its literary values in recent times @xcite . regarding its authorship, a sharp contradiction exists between the dedication at the begin-ning of the book and the colophon at its end, where information about the authorship and printing is provided. joanot martorell affirms in the dedication that he is solely responsible for the work (single-authorship hypothesis), whereas the colophon states that martorell translated the first three of the four parts and that the fourth part was translated by martí joan de galba (dual-authorship hypothesis). here, translation refers to creation, as feigning a translation was commonplace during the period under consideration. the apparent inconsistency has been reconciled supposing that martorell wrote most of the work and galba revised and expanded it later @xcite . nonetheless, this supposition requires empirical validation to verify whether galba actually participated in the creation and, if so, to identify galba's contributions. thus, this study revisits the unsettled authorship attribution of tlb by exploiting parts-of-speech (pos) n-grams as stylistic features. existing literature has only considered a word-length distribution, that of the most frequently used words, and indices of the diversity of vocabulary. this study also addresses the distinction between narration and conversation, which has hitherto been disregarded, for fear that varying proportions of the two components in the work might confound the eventual outcome. we performed exploratory multivariate analyses and demonstrated that, despite internal differences, single authorship is more likely from a statistical point of view. if galba had contributed something to the last quarter of the work, it would have been minimal. the remainder of this paper is organized as follows. in section 2, we review the existing literature and highlight its limitations. section 3 describes the methodology followed in this study. in section 4, we present the experimental results, followed by a discussion in section 5. finally, section 6 concludes the paper. ## related work the single-authorship hypothesis, according to which martorell is the sole author, is based on the description in the dedication, whereas the dualauthorship hypothesis, according to which martorell wrote the first three parts and galba added the fourth, is indicated in the colophon. the single-authorship hypothesis has been endorsed by renowned philologist martí de riquer (de @xcite , although the dualauthorship hypothesis has not been completely rejected @xcite . assuming that the dualauthorship hypothesis is true, the question arises as to where the fourth part that galba purportedly composed begins. tlb is not explicitly divided into four parts, except for the first part, the beginning of which is noted ahead of chapter 1. considering that tlb consists of 487 chapters of unequal length, de @xcite estimated that if the colophon is to be trusted, the fourth part begins with chapter 363 in terms of the number of chapters, or around chapter 283 in terms of the total length of the novel. under these circumstances, stylometry plays a key role @xcite . stylometry aims to identify the genuine author(s) of a written text through quantitative analysis @xcite . a series of stylometric studies have delved into questions concerning the authorship of tlb. in their pioneering study, @xcite examined the distribution of word lengths @xcite and the most frequent context-free words, including articles, conjunctions, prepositions, and pronouns. they detected a change in the distribution of the variables from chapters 371 to 382 and concluded that the results corroborate dual authorship. nonetheless, they admit the possibility that the observed differences may have been due to factors other than changes in authors. one shortcoming of @xcite is that word-length distribution is not currently viewed as the most effective feature for authorship attribution tasks, which is implied by its practical absence in recent studies. furthermore, the linguistic interpretation of word-length distribution is not straightforward. the stylistic information encoded therein is unclear. another drawback is the model selection process for the number of authors involved in the work. they compared two probabilistic models corresponding to the single and dual authorship hypothe-ses. the former consists of a single multinomial distribution, and the latter comprises a mixture of two distributions. then, the ratio of posterior probabilities between the two models was computed to decide which one was more likely. however, they did not consider the model's complexity. hence, the selection of the dual authorship hypothesis was the natural outcome, given that a more complex model fits better than a simpler one. the tradeoff between model complexity and goodness of fit should be addressed appropriately. in addition, the authors disregarded the distinction between narration and conversation when the analyses were vulnerable to the varying proportions of these two components in the work. in fact, the narration/conversation ratio fluctuates greatly among chapters, as depicted in figure 1 . the vertical axis represents the narration ratio, computed as the number of tokens in the narration divided by the chapter length. the curve represents the moving average with a window size of 20. the ratio of narration remains high from around chapter 375 onward to the end, whereas it is negligible from chapters 40-100. we assume that a different proportion of narration/conversation is not per se indicative of different authorship because its constancy across a work by a single author is not self-evident; narration/conversation may well be abundant in some sections and exiguous in others. using analogous approaches, other studies arrived at the same conclusion @xcite @xcite . @xcite also reinforces their findings using eight different indices of the diversity of vocabulary, which is rarely utilized as an effective stylistic feature either. thus, this study intends to shed new light on the authorship attribution of tlb in the following ways: (i) we leverage pos n-grams, which are effective and linguistically interpretable stylistic features; (ii) we conduct model selection appropriately, considering the trade-off between model complexity and goodness of fit; and (iii) we address the distinction between narration and conversation, which has hitherto been omitted. ## methods a digitized transcription of the princeps edition was used in this study @xcite foot_0 . the chapter titles and latin phrases (e.g., deo gracias "thanks to god") were removed. we also eliminated paragraphs in the letter format that deviated from the typical structure of the work. numerous passages allegedly plagiarized from other works (de riquer, 1990) were retained as such for the sake of simplicity. regarding punctuation, commas were eliminated so that editorial interventions would not come into play, whereas periods, colons, semi-colons, interrogation marks, and exclamation marks indicating sentence boundaries were retained as single punctuation symbols. moreover, contracted and concatenated forms were separated prior to pos tagging (e.g., l'art "the art" and donant-lo "giving it" were divided into l' art and donant -lo, respectively). pre-processing resulted in 420,879 tokens and a vocabulary size of 17,181. for subsequent analyses, we did not adopt the original chapter division because the lengths varied considerably from one another. instead, we generated equal-length pieces of 10k tokens to obtain reliable statistics. the length of 10k tokens is way above the minimum sample size of 5k tokens that was shown to be sufficient for stylometric analysis @xcite . the shortest final piece of 879 tokens was merged into the penultimate one. thus, the entire work resulted in forty-two pieces. we leveraged pos n-grams as stylistic features. the effectiveness of pos n-grams has been demonstrated by the previous research addressing literary works in multiple languages, including english @xcite @xcite @xcite @xcite , french @xcite , japanese (uesaka and murakami, 2015), and spanish @xcite . the advantages of employing pos sequences are multi-fold: (i) the numerous occurrences provide reliable statistics; (ii) they are relatively, if not completely, independent of content; (iii) they are deemed to be reliable style markers @xcite @xcite . although partially, they capture syntactic patterns that are difficult to imitate and allegedly out of the conscious control of the author @xcite ; and (iv) they are supposedly less vulnerable to editorial interventions that would manipulate the original; in fact, orthographic vacillation could derive not only from the author but also from the typesetters in the middle ages. the tokens were pos-tagged according to lemmatized concordance foot_1 . specifically, we looked up each token in the concordance prepared in keywords in context format, considering its preceding and following contexts. thus, more than 99% of the tokens were correctly tagged. tokens that were ambiguous or left untagged were assigned a special tag, unk, for simplicity, although manual tagging was desirable. consequently, the number of pos tags amounted to thirteen foot_2 . for the most frequent twenty words, including adverbs, conjunctions, prepositions, and verbs, we adopted lemma forms in lieu of the pos-tags to exploit their particular usage 4 . for example, the preposition de "of" was not converted into prep but maintained as such. this resulted in thirty-three unigram types in total: thirteen pos tags and twenty lemma forms. for the subsequent multivariate analyses, every text piece was represented as a vector, with its elements being the z-transformed relative frequencies of the n-grams @xcite . the relative frequencies were standardized to have a zero mean and unit variance for every variable. we considered only the most frequent pos n-grams above a given rank threshold r, whereas the remainder was aggregated under the others label. thereafter, we performed two exploratory multivariate analyses, i.e., principal component analysis (pca) and k-means clustering. as no other works by the relevant authors were available, it was infeasible to apply supervised methods such as classification. to assess the robustness of the analyses, we varied the n-gram size n for @xmath0, 2, 3, 4} and the rank threshold r for @xmath1, 100, 300, 500}. for @xmath2, r was fixed at 33, which is the number of unigram types. ## results and analyses in this section, we present the experimental results without a narration/conversation distinction. the results of the respective parts will be presented in section 5.1. for illustrative purposes, we provide the results obtained with the hyper-parameters (n, r) = (3, 300), unless noted otherwise. first, we examined the overall similarity patterns across the entire work. figure 2 displays the pairwise distance scores between the pieces. the i-th piece is designated as tlb i. the scores were calculated as ## conclusions and future work this study revisited the unsettled authorship attribution of tirant lo blanc using stylometric techniques; specifically, we exploited pos n-grams as stylistic features. furthermore, we addressed the distinction between narration and conversation, which has hitherto been omitted. we performed exploratory multivariate analyses and demonstrated that, despite internal differences, single-authorship is more likely from a statistical point of view. if galba had contributed something to the last quarter of the work, it would have been minimal. one limitation of our study is the adoption of rather coarse granularity in parts-of-speech. for instance, we did not distinguish between verbal forms such as finite forms, infinitive, gerund, and participle and instead treated them all under the category of verb. however, their peculiar usage has been pointed out in previous literature @xcite @xcite and so could be useful for detecting authorial fingerprints as well. furthermore, it will be intriguing to explore the orthographic, lexical, morphological, and syntactic traits that have been suggested as distinctive in previous research @xcite @xcite @xcite , to name a few foot_8 . moreover, two hypotheses concerning the genesis of tlb remain to be examined stylometrically: (i) that a short fragmentary manuscript denominated guillem de vàroich was actually written by martorell @xcite ; and (ii) that the valencian writer joan roís de corella is the genuine author of tlb @xcite .