Stylometry

..or how do you know it's Shakespeare?

Стил(о|е)метрия

But first a reminder:

danilsko.github.io/DHelsinki

Stylometry

is the statistical analysis of variations in literary style between one writer or genre and another

Oxford Dictionary

in all their variety of material and method, have two features in common: the <...> texts they study have to be coaxed to yield numbers, and the numbers themselves have to be processed via statistics.

M. Eder, M. Kestemont, J. Rybicki. ‘Stylo’: a package for stylometric analyses

Stylometric studies

underlying stylometric studies is that authors have an unconscious as well as conscious aspect to their style

Encyclopaedia of Statistical Sciences

The main assumption

How?

По-видимому, в разных стилях книжной и разговорной речи <...> частота употребления разных типов слов различна. Точные изыскания в этой области помогли бы установить структурно-грамматические, а отчасти и семантические различия между стилями <...>

В.В. Виноградов (1938) Введение в грамматическое учение о слове

It's mostly about frequencies

Words/word forms
- especially function words
Symbol N-grams
POS tags
Syntactic structures
Metric structures

Frequencies of

general vocabulary diversity
hapax legomena (see A. Q. Morton. 'Once. A Test of Authorship Based on Words Which Are Not Repeated in the Sample')
sentence length
punctuation
(in unedited text) spelling mistakes and specifics

Other features

Why?

Motivation, or why try and measure style?

Authorship disputes
Exploring genre differences
Co-authorship studies
Exploring gender/age differences
Capturing human stylome/idiostyle
Translation studies
Forensic linguistics, security and anonymity

Origins

authorship disputes and the rise of quantitative research on style
early stylostatistics/stylometrics/stylometry
XX century: from failures to successes

Authorship disputes

Presumably, each national literature has its own famous unsolved attribution case, such as the Shakespearean canon, a collection of Polish erotic poems of the 16th century ascribed to Mikołaj Sęp Szarzyński, the Russian epic poem The Tale of Igor’s Campaign, and many other.

Eder M. (2011) Style-markers in authorship attribution: A cross-language study of the authorial fingerprint.

Authorship disputes

Presumably, each national literature has its own famous unsolved attribution case, such as the Shakespearean canon, a collection of Polish erotic poems of the 16th century ascribed to Mikołaj Sęp Szarzyński, the Russian epic poem The Tale of Igor’s Campaign, and many other.

Eder M. (2011) Style-markers in authorship attribution: A cross-language study of the authorial fingerprint.

Слово о полку Игореве

Уже двести лет не прекращается дискуссия о том, что представляет собой «Слово о полку Игореве», — подлинное древнерусское произведение или искусную подделку под древность, созданную в XVIII веке. <...> Гибель единственного списка этого произведения лишает исследователей возможности произвести анализ почерка, бумаги, чернил и прочих материальных характеристик первоисточника. Наиболее прочным основанием для решения проблемы подлинности или поддельности «Слова о полку Игореве» оказывается в таких условиях язык этого памятника.

A.А. Зализняк. "Слово о полку Игореве": взгляд лингвиста.

А. А. Зализняк

tvkultura.ru

Attribution through style

Lorenzo Valla (1407 – 1457)

Italian humanist, rhetorician, educator and Catholic priest
in 1439 proved that the Donation of Constantine was a forgery
demonstrated that it could not have been written in the era of Constantine I (IV century), as its style dated to XIII century

wikipedia.org

Quantifying style

1851 — A. De Morgan suggests mean word-length as an authorship feature
1873 — New Shakespeare Society (Furnival, Fleay et al)
1887 — T. Mendenhall, The Characteristic Curves of Composition, the first known work on quantitative authorship attribution

Early stylometry

1867 — Campbell L. The Sophisties and Polilicus of Plato.
1880 — W. Dittenberger,

Sprachliche Kriterien für die Chronologie der Platonischen Dialoge
1890 — W. Lutosławski, Principes de stylométrie

Early stylometry in Russia

1915 — Морозов Н.А. Лингвистические спектры (likely inspired by Lutoslawski)
Acknowledges the importance of function words (see pic.)

The amazing Morozov

So this guy wrote 'The Linguistic Spectres'

Ему оппонировал сам Марков (the Markov!)
1916 — Марков А.А. Об одном применении статистического метода ('On the application of a certain statistical method')

Stylometry advances

1937 — Bolling, G.M. The Past Tense of 'To Be' in Homer
1938 — Carroll, J.B. Diversity of vocabulary and the harmonic series law of word-frequency distribution

From spoofs & failures...

in 1901 a scholar attempted to use John Fletcher's preference for "'em," the contractional form of "them," as a marker to distinguish between Fletcher and Philip Massinger in their collaborations—but he mistakenly employed an edition of Massinger's works in which the editor had expanded all instances of "'em" to "them"
A lot of speculation on Shakespeare could not stand scientific tests

...to successes

the breakthrougs came in the 1960-ies, as usual

Federalist papers

12 disputed papers (Hamilton or Madison)
Mosteller F., Wallace D., (1963) Inference in an Authorship Problem.
'<...> to solve the authorship question of The Federalist papers; and to propose routine methods for solving other authorship problems'.

Mosteller, Wallace, 1963

The function words of the language appear to be a fertile source of discriminators, and luckily the high-frequency words are the strongest.
<...>it is important to have a variety of sources of material, to allow “between writings” variability to emerge

Mosteller, Wallace, 1963

In summary, the following points are clear:

Madison is the principal author. These data make it possible to say far more than ever before that the odds are enormously high that Madison wrote the 12 disputed papers. <...>
<...> While choice of underlying constants (choice of prior distributions) matters, it doesn’t matter very much, once one is in the neighborhood of a distribution suggested by a fair body of data.

Yep, size matters!

Размер имеет значение

J. F. Burrows

Most readers and critics behave as though common prepositions, conjunctions, personal pronouns, and articles — the parts of speech which make up at least a third of fictional works in English — do not really exist. But far from being a largely inert linguistic mass which has a simple but uninteresting function, these words and their frequency of use can tell us a great deal about the characters who speak them.

Preface to Computation into Criticism, 1987

Burrows Delta

Benchmark since 2002
Makes use of most frequent words/char.n-grams (though more complex features are also possible)
Has relatively simple mathematics behind (counting z-scores)

Z-score

Text

where

x – frequency of a word
µ - mean frequency of a word in the whole corpus (collection of texts)
σ - standard deviation

This actually works!

I checked for Russian:

This actually works!

Using Delta for authorship attribution

Для всего тренировочного корпуса вычисляется N наиболее частотных слов; сохраняется частотность каждого.
Далее для каждого текста в обеих выборках вычисляется z-score каждого слова
z-score текстов из тестовой выборки сравниваются с z-показателями тренировочной
обнаруживается текст из тренировочной, наиболее близкий классифицируемому.
Его автор и объявляется автором классифицируемого текста.

Meanwhile in (Soviet) Russia

Виноградов В. В. (1961) Проблема авторства и теория стилей
Мартыненко Г.Я. (1988) Основы стилеметрии (a monograph)
Мухин М.Ю. (2011) Лексическая статистика и идиостиль автора: корпусное идеографическое исследование на материале произведений М. Булгакова, В. Набокова, А. Платонова и М. Шолохова
М. Ю. Михеев, Л. И. Эрлих (2017 доклад). Идиостиль и определение авторства текста по частотам служебных слов (people basically reinvented Delta... 🚲 🚲)

Modern stylometry

state of the art

Who wrote 'To Kill a Mockingbird'?

Харпер Ли

Oh, Real-Lee?

А Харпер ли?

Two books

Harper Lee and others

Тэй Хохоф

Труман Капоте