Summary:  The Effectiveness of the Stylometry of Function Words in
          Discriminating between Shakespeare and Fletcher
 
Thomas Bolton Horton
University of Edinburgh, Department of Computer Science
Ph.D. Dissertation, 1987
 
Current Address:
    Dept of Computer Science
    Florida Atlantic Universtiy
    Boca Raton, FL 33431
    407/367-2674
    Internet:  tom@cs.fau.edu   BITNET: HortonT@fauvax
 
 
 
A number of recent successful authorship studies have relied on a statistical
analysis of language features based on function words.  However, stylometry has
not been extensively applied to Elizabethan and Jacobean dramatic questions.
To determine the effectiveness of such an approach in this field, language
features were studied in twenty-four plays by Shakespeare and eight by
Fletcher. The goal was to develop procedures that might be used to determine
the authorship of individual scenes in _The Two Noble Kinsmen_ (TNK) and
_Henry VIII_ (H8).
 
Of the 32 texts of known authorship, 6 were set aside as a test set. These were
treated as if their authorship was unknown.  All procedures that I evaluated
were applied to samples from these 6 plays, and these results were used to
judge their effectiveness.  The remaining 20 Shakespeare texts and the 6
Fletcher texts made up the control set, which was used to establish each
dramatist's characteristics of composition.
 
Homonyms, spelling variants and contracted forms in old-spelling dramatic texts
present problems for a computer analysis.  Many common function words have
several variant spellings (e.g. "been" can be spelled "beene", "bene", "bin"
etc).  Other forms can represent a number of lexical forms; for example,
besides the indefinite article, the single-letter word "a" can mean "he," "of,"
"on," "ah" etc.  Some forms of compound contractions involving function words
are frequent (for example, "let's", "o'th'", "'tis" and the many contracted
forms of "is" like "it's", "Caesar's", "he's" etc).
 
A program (called REPLACE) that uses a system of pre-edit codes and
replacement/expansion lists was developed to prepare versions of the texts in
which all forms of common words can be recognized automatically.  Homonyms and
variants were found and marked in each text using a system of hash suffixes.
For example, "a#1" represents occurrences of "he", "a#3" represents "on", etc.
Occurrences of "beene", "bene", etc are replaced by the standard form (but
occurrences of "bin" meaning a container are marked "bin#1"). In addition, a
list of compound contractions and their full forms was compiled (from
experience and with help from Partridge's book _Orthography in Shakespeare and
Elizabethan Drama_).  A simple replacement strategy is not powerful enough to
handle apostrophe-s and -t forms.  Hash suffixes were also used to distinguish
apostrophe-s contractions involving "is", "us", "his" etc from possessive
forms, and contractions of "it" from forms like "banish`t" (ie "banished").
 
Program REPLACE made use of these special markings and the expansion lists to
prepare "expanded" versions of the plays.  These versions were then used to
determine the extent of each author's use of compound contractions.  In almost
every case, Fletcher uses more of these forms than Shakespeare, although the
latter uses more contractions as his career progresses.  Because of this
secular change and the possibility of alterations introduced by scribes,
compositors or revisors, the expanded versions of the plays were used in
remainder of the study.
 
To evaluate some procedures for determining authorship developed by A. Q.
Morton and his colleagues, occurrences of 30 common collocations and 5
proportional pairs are analyzed in the texts.  Within-author variation for
these features is greater than had been found in previous studies.  Univariate
chi-square tests are shown to be of limited usefulness because of the
statistical distribution of these textual features and correlation between
pairs of features.  Contrary to some earlier claims, the best of the
collocations do not discriminate as well as most of the individual words from
which they are composed.
 
Turning to the rate of occurrence of individual words and groups of words,
distinctiveness ratios and t-tests are used to select variables that best
discriminate between Shakespeare and Fletcher.  Variation due to date of
composition and genre within the Shakespeare texts is examined using the
statistical procedure analysis of variance.  A number of potential markers of
authorship were eliminated because the rate of use for one of the subgroups
(such as comedies, or late plays) was too close to Fletcher's overall rate.
Some of the observed variations are interesting in their own right.
Shakespeare's comedies are characterized by high rates for pronouns and "a",
together with low rates for "the". Tragedies have low rates for "a".  The
histories have very low rates for personal pronouns (as noted by Brainerd) and
high rates for "in", "of" and "and". "In" occurs infrequently in the romances,
while "so" is much more frequent in this genre than the other three. The late
plays have a high rate for "the".
 
The rates for several word classes were examined (pronouns, forms of "have",
"be" and "do", and modal verbs), but none of these group variables proved
useful.  However, when compiling the list of spelling variants, I noticed that
Shakespeare uses more forms that begin with "there-" or "where-" (such as
"therefore", "therein", "wheresoever", etc); the forms that Fletcher does use
occur less frequently than in Shakespeare's texts.  When the rates for all
these "there/where- compounds" are combined, Shakespeare's overall rate is
almost 12 times that of Fletcher.  These forms are rather infrequent, and some
forms appear in stock phrases or songs and may not reflect the author's normal
usage; for these reasons, this group was not used as a variable in the main
analysis of function words.  However, two scenes usually attributed to
Fletcher, _Henry VIII_ I.iii and _The Two Noble Kinsmen_ IV.iii, contain what I
feel are significant occurrences of there/where- compounds.  (Later analysis
indicated that the use of function words in both scenes is also much closer to
Shakespeare's known work.)
 
A multivariate and distribution-free discriminant analysis procedure (using
kernel estimation) was used to determine if data from a single scene resembled
the scenes from Shakspeare or Fletcher more closely.  The classifiers based on
the best marker words and the kernel method were carefully evaluated using the
texts of known authorship.  To study the effect of characterization, I
extracted the speeches of 62 characters (who speak at least 500 words) from 6
test-set plays.  The procedure was only slightly less accurate in classifying
these character samples than the set of test-set scenes, which suggests that
characterization does not affect the use of these word-rate variables with this
procedure to any great degree (at least for the purpose of distinguishing
Fletcher from Shakespeare).  I also tested the procedures with smaller and
smaller scenes, and found that they performed well for samples as short as 500
words. When the final procedure is used to assign the 459 scenes of known
authorship (containing at least 500 words), 94.8% are assigned to the correct
author.  Only two scenes are incorrectly classified, and 4.8% of the scenes
cannot be assigned to either author by the procedure.
 
When applied to individual scenes of at least 500 words in _The Two Noble
Kinsmen_ and _Henry VIII_, the procedure indicates that both plays are
collaborations and generally supports the usual division.  However, the marker
words in a number of scenes often attributed to Fletcher are very much closer
to Shakespeare's pattern of use.  Some of the more interesting results include
the assignment to Shakespeare of TNK IV.iii, which most scholars have regarded
as decent imitation.  (The function word result for this scene is supported to
some extent by an occurrence of a there/where- compound and by rates for "hath"
and "you" that are unlike rates in known Fletcher scenes.)  In H8, I.iii is
another scene that resembles Shakespeare in the use of function words and
there/where- compounds.  It also contains a number of convincing Fletcher
stylistic traits, so perhaps revision should be proposed.
 
The function-word results for Shakespeare are extremely strong for the prose
scene V.iv, which contains occurrences of "ye" and "'em" (Fletcher traits) that
are unparalleled in Shakespeare's texts.  This contradictory evidence raises
questions about the copy-text; again, revision is a plausible explanation
(although the results are so strong in this case that the scene appears to be
mainly Shakespeare's work).  The function-word results support Foakes' and
Hoy's suggestions that Fletcher touched up Shakespeare's work in II.i-ii,
III.iib, and IV.i-ii.  The use of function words in Act IV is very unlike
Fletcher, and my results indicate that he had little or nothing to do with it.
Results for II.ii and III.iib are less clear but may support the theory of
revision.
 
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Department of Computer Science, Florida Atlantic University, Boca Raton, FL
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