Stylometry
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Stylometry is the application of the study of linguistic style, usually to written language. In the last few years it has successfully been applied also to music and to fine-art paintings.
Stylometry is often used to attribute authorship to anonymous or disputed documents. It has legal as well as academic and literary applications, ranging from the question of the authorship of Shakespeare's works to Forensic linguistics.
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[edit] History
Stylometry grew out of earlier techniques of analyzing texts for evidence of authenticity, authorial identity, and other questions. An early example is Lorenzo Valla's 1439 proof that the Donation of Constantine was a forgery, an argument based partly on a comparison of the Latin with that used in authentic 4th Century documents.
The modern practice of the discipline received major impetus from the study of authorship problems in English Renaissance drama. Researchers and readers observed that some playwrights of the era had distinctive patterns of language preferences, and attempted to use those patterns to identify authors in uncertain or collaborative works. Early efforts were not always successful: in 1901, one researcher 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."[1]
The development of computers and their capacities for analyzing large quantities of data enhanced this type of effort by orders of magnitude. The great capacity of computers for data analysis, however, did not guarantee quality output. In the early 1960s, Rev. A. Q. Morton produced a computer analysis of the fourteen Epistles of the New Testament attributed to St. Paul, which showed that six different authors had written that body of work. A check of his method, applied to the works of James Joyce, gave the result that Ulysses was written by five separate individuals, none of whom had any part in A Portrait of the Artist as a Young Man.[2]
In time, however, and with practice, researchers and scholars have refined their approaches and methods, to yield better results. One notable early success was the resolution of disputed authorship in twelve of the Federalist Papers by Frederick Mosteller and David Wallace.[3] While questions of initial assumptions and methodology still arise (and, perhaps, always will), few now dispute the basic premise that linguistic analysis of written texts can produce valuable information and insight. (Indeed, this was apparent even before the advent of computers: the successful application of a textual/linguistic approach to the Fletcher canon by Cyrus Hoy and others yielded clear results in the late 1950s and early '60s.) An example of a modern study is the analysis of Ronald Reagan's radio commentaries of uncertain authorship.[4]
[edit] Methods
Modern stylometry draws heavily on the aid of computers for statistical analysis, artificial intelligence and access to the growing corpus of texts available via the Internet. Software systems such as Signature (freeware produced by Dr Peter Millican of Oxford University) make its use increasingly practicable, even for the non-expert.
Whereas in the past, stylometry emphasized the rarest or most striking elements of a text, contemporary techniques can isolate identifying patterns even in common parts of speech.
[edit] Writer invariant
The primary stylometric method is the writer invariant: a property of a text which is invariant of its author. An example of a writer invariant is frequency of function words used by the writer.
In one such method, the text is analyzed to find the 50 most common words. The text is then broken into 5,000 word chunks and each of the chunks is analyzed to find the frequency of those 50 words in that chunk. This generates a unique 50-number identifier for each chunk. These numbers place each chunk of text into a point in a 50-dimensional space. This 50-dimensional space is flattened into a plane using principal components analysis (PCA). This results in a display of points that correspond to an author's style. If two literary works are placed on the same plane, the resulting pattern may show if both works were by the same author or different authors.
[edit] Neural networks
Neural networks are used to analyze authorship of texts. One such network was built with the links having random strengths. The network was presented with training texts of known authorship. Any time the network guessed incorrectly, it adjusted the strengths of its links until the network could properly identify known texts. Once the training period is complete, the network can properly determine authorship of texts by authors that it had been trained on previously.
[edit] Genetic Algorithms
The genetic algorithm is another artificial intelligence technique used in stylometry. A method starts out with a set of rules. An example rule might be, "If but appears more than 1.7 times in every thousand words, then the text is author X". The program is presented with text and uses the rules to determine authorship. The rules are tested against a set of known texts and each rule is given a fitness score. The 50 rules with the lowest scores are thrown out. The remaining 50 rules are given small changes and 50 new rules are introduced. This is repeated until the evolved rules correctly attribute the texts.
[edit] Rare Pairs
One method for identifying style is called "rare pairs", and relies upon individual habits of collocation. The use of certain words may, for a particular author, idiosyncratically entail the use of other, predictable words.
[edit] Notes
- ^ Samuel Schoenbaum, Internal evidence and Elizabethan dramatic authorship; an essay in literary history and method, p. 171.
- ^ Samuel Schoenbaum, Internal evidence and Elizabethan dramatic authorship; an essay in literary history and method, p. 196.
- ^ F. Mosteller and D. Wallace (1964). Inference and Disputed Authorship: The Federalist. Reading, MA: Addison-Wesley.
- ^ Edoardo M. Airoldi, Stephen E. Fienberg, Kiron K. Skinner (July 2007). "Whose Ideas? Whose Words? Authorship of Ronald Reagan's Radio Addresses". PS: Political Science & Politics 40 (3): 501–506. doi:.
[edit] References
- Can, F., Patton, J. M. "Change of writing style with time." Computers and the Humanities. Vol. 38, No. 1 (2004), pp. 61-82.
- Hope, Jonathan. The Authorship of Shakespeare's Plays. Cambridge, Cambridge University Press, 1994.
- Hoy, Cyrus. "The Shares of Fletcher and His Collaborators in the Beaumont and Fletcher Canon." Studies in Bibliography 7-15, 1956-62.
- Kenny, Anthony. The Computation of Style: An Introduction to Statistics for Students of Literature and Humanities. Oxford, Pergamon Press, 1982.
- Romaine, Suzanne. Socio-Historical Linguistics. Cambridge, Cambridge University Press, 1982.
- Samuels, M. L. Linguistic Evolution: With Special Reference to English. Cambridge, Cambridge University Press, 1972.
- Schoenbaum, Samuel. Internal Evidence and Elizabethan Dramatic Authorship: An Essay in Literary History and Method. Evanston, Il., Northwestern University Press, 1966.
See also the academic journal Literary and Linguistic Computing (1986– ), published by the University of Oxford, and the journal Language Resources and Evaluation.
