Supervised Machine Learning for Hybrid Meter Alex Estes & Christopher Hench University of California, Berkeley Department of German Berkeley, CA 94720, USA estes,chench @berkeley.edu { } Abstract cess of determining the metrical value of each sylla- ble for a line of poetry). In applying machine learn- Following classical antiquity, European poetic ing techniques to scan syllables of a hybrid meter, meter was complicated by traditions negotiat- we believe we can contribute to the study of both ing between the prosodic stress of vernacular metrics and poetics, medieval and otherwise. Our dialects and a classical system based on syl- system serves not only pedagogical purposes by in- lable length. Middle High German (MHG) epic poetry found a solution in a hybrid qual- troducing students to the meter of medieval German itative and quantitative meter. We develop a epic poetry, but also presents itself as a tool for fur- CRF model to predict the metrical values of ther research in author identification or topic model- syllables in MHG epic verse, achieving an F- ing metrical form. score of .894 on 10-fold cross-validated devel- To illustrate quantitative meter, we consider the opment data (outperforming several baselines) epic poetry of Latin and Greek. Each line consists and .904 on held-out testing data. The method of six feet, each foot typically a dactyl (a long sylla- used in this paper presents itself as a viable op- tion for other literary traditions, and as a tool ble followed by two short syllables) or spondee (two for subsequent genre or author analysis. long syllables). A syllable is considered long if it has a long vowel or diphthong, or ends in a conso- nant (Hayes, 1989). All other syllables are short. 1 Introduction The first line of Virgil’s Aeneid serves as example:2 The divergence of Latin into distinct regional di- arma¯ vi rumque ca no,¯ Tro jae qui¯ primus¯ ab or¯ is¯ | | | | | — ^^ — ^ ^ —— —— — ^ ^ —— alects had profound linguistic and literary impli- | | | | | cations for all of Europe. Even before the Mid- Shakespeare’s verse, on the other hand, exhibits dle Ages, the syllable length of classical Latin had qualitative meter, structured in iambic pentameter, been nearly forgotten in the vernacular.1 Latin po- where each line has five iambs (a bisyllabic foot con- etry had used quantitative meter, whereby syllable sisting of an unstressed first syllable followed by a length was the organizing principle. However, the stressed second syllable). The first line of Romeo emerging dialects differed from Latin in that stress and Juliet is scanned below:3 became a phonologically important feature, and so- called qualitative meter predominated. In order to Two house holds, both alike in dig nity. | | | | | | reconcile these linguistic differences, poetic forms ´ ´ ´ ´ ´ | × × | × × |×× |× × |× ×| emerged in which meter relied on both stress and syllable length. These hybrid metrical forms pose 2 Middle High German Meter unique challenges to automated scansion (the pro- This paper considers the meter of twelfth and thir- 1Augustine writes toward the end of the fourth century that teenth century Middle High German (MHG) epic while he recognizes time intervals, he can no longer distinguish between long and short syllables: syllabarum longarum et bre- 2— represents a long syllable and ^ a short syllable. vium cognicionem me non habere... “I cannot recognize long 3Every syllable is marked with . The acute accent ´ marks × and short syllables...” cf. Augustinus, De musica, III, 3, 5. stress. 1 Proceedings of the Fifth Workshop on Computational Linguistics for Literature, NAACL-HLT 2016, pages 1–8, San Diego, California, June 1, 2016. c 2016 Association for Computational Linguistics verse. Although written in a Germanic language, etic tradition than in its phonological definition. If a MHG poetry was greatly influenced by the Romance foot has only one syllable, the syllable must be long tradition. This heritage is evident in its hybrid metri- because a long syllable is two morae and the MHG cal structure: MHG verse patterns according to both foot requires two morae. A short syllable cannot be syllable stress and length (Bostock, 1947). the only syllable in a foot, since it cannot be two The predominating pattern is an alternation be- morae. If a foot has three syllables, two must be tween stressed and unstressed syllables (Tervooren, short because only short syllables can be scanned as 1997).4 MHG epic verse employs trochaic tetrame- half morae, together forming one mora.7 The other ter: each line has four feet (Bostock, 1947), and each syllable is analyzed as one mora, yielding the re- foot is a trochee. Phonologically, a trochee consists quired two morae in the foot. To summarize, a syl- of two syllables; the first syllable is stressed, and lable can have one of three length values: mora, half the second is unstressed. For example, the English mora, or double mora. A half mora must be phono- word “better” is a trochee, but the word “alive” is logically short, and a double mora must be phono- not. The famous Longfellow epic poem The Song of logically long. Phonological length is otherwise ir- Hiawatha is written in trochaic tetrameter, and the relevant and any syllable can be one mora. first line serves to illustrate this rhythm: In addition to length, as a function of morae, syl- lables are also assigned stress. There are three stress Should you ask me, whence these stories? values: primary, secondary, or unstressed. Primary ´ ´ ´ ´ | × × | × × | × × | × × | stress is assigned to the first or only stressed sylla- Similarly, the typical MHG epic verse foot is two ble in a word. Secondary stress is assigned to any syllables in length, a stressed syllable followed by an following stressed syllable(s) in that word. All other unstressed syllable. However, feet can also be filled syllables are unstressed.8 by one or three syllables (Domanowski et al., 2009). The final mora of the final foot of a line is omitted If a foot is filled by one syllable, the syllable must by convention. This is construed as a pause, and be phonologically long. If the foot is filled by three receives its own symbol in the scansion, even though syllables, either the first two or the last two syllables there is no corresponding word or syllable. A short, must both be phonologically short. word final syllable may also be elided before a word It is in these atypical feet that the influence of beginning with a vowel. MHG epic verse permits up quantitative meter, where syllable length is the key to three syllables in anacrusis (a series of syllables factor, becomes evident. We must slightly redefine at the beginning of a line that do not count in the the foot to account for this. Syllable length is mea- meter). These syllables may or may not carry lexical sured in morae. Phonologically, a mora is a unit of or syntactic stress, but they are always scanned as time such that a short syllable has one mora and a unstressed morae. long syllable has two morae (Fox, 2000).5 A foot in The above features yield eight possible metrical this meter is more precisely defined as having two values for any syllable: morae, not necessarily two syllables.6 Indeed, the mora, not the syllable, has been called the funda- mental unit of MHG verse (Tervooren, 1997, p. 1), although the mora functions differently in this po- 4There is no consensus view on MHG meter. For this work we have most closely followed the viewpoints presented by Do- 7Occasionally very weakly stressed long syllables can also manowski et al. (2009) and Heusler (1956), as well as more count as a half mora. explicitly addressed the function of morae. 8The metrical distinction between different degrees of stress 5For example, the English word “red” has two morae since is rooted in phonological reality (Giegerich, 1985): in a word it ends in a consonant, whereas the first syllable in the English with many syllables, one syllable usually has a primary stress, word “reduce” has one mora, since it ends in a short vowel. and the others have either secondary or weak stress. For exam- 6It can be helpful to think of MHG meter in the musical ple, many pronounce the English word “anecdotal” with sec- sense. Each foot is a measure of 2/4 meter, where one mora is ondary stress on the first syllable, primary stress on the third equivalent to one quarter note (Bogl,¨ 2006). syllable, and weakest stress on the second and fourth syllables. 2 mora - primary stress ( ´ ): a syllable with pri- 3 Previous Computational Approaches to • × mary stress Meter mora - secondary stress ( ` ): a syllable with • × There are two prevailing treatments of meter in the secondary stress literature concerned with computational poetic text mora - unstressed ( ): an unstressed syllable • × analysis. One approach takes a known meter and as- half mora - primary stress (^´ ): a short sylla- signs syllables to stress patterns based on such pa- • ble with primary stress; according to metrical rameters (Hartman, 1996). The second approach convention the preceding syllable must be long assumes nothing of the meter, and seeks to deter- half mora - secondary stress (^` ): a short syl- mine it by marking syllables and identifying pat- • lable with secondary stress terns (Plamondon, 2006; McAleese, 2007; Greene et al., 2010; Agirrezabal et al., 2013; Navarro, 2015). half mora - unstressed (^): a short unstressed • Our approach draws more on the latter. syllable Previous scholarship has focused on relatively double mora (—): a stressed long syllable; • simple systems of meter and adopted rule-based, sta- double morae always carry primary stress tistical, or unsupervised approaches. The hybrid na- elision (e): an elided syllable • . ture of MHG meter, and other complex systems de- Line 1 of Hartmann von Aue’s Der arme Hein- veloping out of classical antiquity, makes it difficult 14 rich is prototypical.