An Examination of the Authorship Attributions of Two Major Roman Authors

Introduction
This paper describes a stylometric analysis of 16 texts
attributed by the manuscript tradition to two Roman
authors of the first century BCE: Gaius Julius Caesar (100-44;
all dates BCE, unless noted), and Gaius Sallustius Crispus,
commonly referred to as Sallust (86-34). The 'control' consists
of the Lives of the Twelve Caesars of Gaius Suetonius
Tranquillus (77-121 CE at the earliest). All twelve works are
attributed by the tradition to Suetonius, and our analysis, given
in earlier publications, has corroborated this tradition of single
authorship.
The texts analysed include the fourteen books attributed to
Caesar, and two books by Sallust. The texts of Caesar comprise:
the eight books on the war in which he conquered Gaul in the
years from 58 to 50; the three books on the following Civil
Wars (49-48), in which Caesar eliminated his great political
rival Pompey and his Eastern army; and the three books on his
final battles against the surviving generals: in Alexandria
(48-47), Africa (47-46), and Spain (46-45). This study then
completes a similar analysis of the works of Sallust: the war in
Africa against the Numidian king Jugurtha (111-106); and the
failed rebellion of the Roman noble Lucius Sergius Catilina,
known as Catiline, in 63.
Of the eight books of the Gallic Wars, the question arises as to
exactly when and by whom they were created. Some have
argued that the first seven were written as a group, but that the
eighth must be attributed to his general Hirtius, who claims in
the work that he was responsible for both that and the later text
on the war in Alexandria.
Of the further works, the three on the Civil Wars, from his
crossing of the Rubicon in 49, to the battle of Pharsalus in
Thessaly in 48, are generally accepted to have been authored
by Caesar. There is considerable disagreement, however,
concerning the three wars in Egypt, Africa and Spain: the
Alexandrian War, as noted, is claimed by Hirtius; the origin of
the African War is uncertain; and the internal character of the
text of the Spanish War clearly defines it to be the creation of
an unknown person. There is little disagreement on this last
score, since the text on the Spanish War comprises some of the
worst Latin extant, and was probably intended to be the raw
material for a more structured history.
Statistical Routines
The Stylometric Analysis of the 28 texts has been
conducted by use of the SPSS routines Hierarchical
Cluster Analysis, and Principal Component Analysis.
Discriminant Analysis has then been used to test the group
memberships suggested by the first two.
Data
The data for the statistical routines have been provided by
a matrix of 9,000 by 58 real-valued elements that
represent the normalized frequencies of occurrence of unique
lemmas (dictionary head-words) in 58 texts. This matrix has
been generated from the fully disambiguated texts of the 58
works of Caesar, Sallust, Suetonius, and the Scriptores
Historiae Augustae, and involves a reduction from 329,000 to
305,000 numeric values to be handled after the removal of all
proper nouns. This matrix has been sorted in decreasing order
on the frequencies of lemmas, and lists also the number of texts
in which each individual lemma is not found. It has therefore
been easy to choose for analysis the most frequent function
words, verbs, nouns & pronouns, and adjectives in the texts
under consideration.
The main thrust of the research has been conducted on the data
set of function words, but, because the most frequent verbs,
nouns, and adjectives can be identified so accurately in a
disambiguated and tagged text, it has been possible to compare
the statistical results of these three parts of speech with those
from function words, which themselves are considered in the
literature to be standard as data in stylometric analysis. The
first thing noticed, however, has been the necessity of
comparing the results from a full set of lemmas, with a set from
which the most frequent 2 or 3 have been removed. These few
very frequent lemmas can apparently overwhelm the effects of
the other lemmas, and skew the results slightly, but noticeably.
Analysis
I n a test of 37 function lemmas (with the removal of the
three most frequent: et, in, and the separable suffix que), the twelve works of Suetonius, the 'control' works, demonstrate
that the lives remain closely grouped, as found in our earlier
research, with only the life of Titus being slightly removed
from all others. When all 40 of the top function lemmas are
involved, however, there are slight changes in the distances of
most lives, and the life of Otho joins that of Titus at the further
remove, although this removal does not involve any question
of a change of authorship.
In an analysis of Sallust's Catiline and the Jugurthan War, the
results from an analysis of the 37 most common function
lemmas reinforce the manuscript tradition of authorship, with
a very close association; with all 40 of the most frequent
lemmas, however, the relative spacing of the two works
approaches even a possible difference in authorship.
The analysis of 37 of the 40 most common function lemmas in
the works of Caesar provides a greater complexity. There is,
first of all, a very close association between Gallic VIII and
the Alexandrian War, with both being clearly separated from
most of the other works attributed: an apparently clear
vindication of the claims by Hirtius to be the author of both.
The Spanish War, that work of execrable Latin, is obviously
of totally separate authorship. The most remarkable result,
however, is the distance between Book I of the Gallic Wars
(that book with the famous beginning: "Gallia est omnis divisa
in partes tres" - "All Gaul is divided into three parts" ), and the
other works attributed to Caesar (other than the Spanish War).
Figure 1
Figure 2
Figure 3
When all 40 top function lemmas are employed, most
separations between the works attributed to Caesar increase.
Gallic I and Gallic IV are now both at a further remove from
the other works, and are hardly within reasonable attribution
to Caesar. The Alexandrian War, however, is now very close
to other texts, and far from Gallic VIII; and both the African
War and Gallic VIII are now possibly beyond any reasonable
attribution to Caesar, although the attribution of Gallic VIII to
Hirtius remains possible. The Spanish War continues to be far
distant from any other work in the 28 studied.
The analyses of verbs, nouns, and adjectives, all demonstrate
considerable differences amongst the works. For example,
Gallic VIII and the Alexandrian War become relatively distant
in the analysis of nouns (less the top three), although they are still closer to one another than to any other works. In the
analysis of adjectives, however, they appear no longer to be
related, and in addition, Gallic VIII becomes quite close to
several other books of the Gallic Wars and Civil Wars.
Conclusions
I t appears clear that the arguments in the stylometric
literature, describing the necessity of using function lemmas,
remain valid. Nonetheless, verbs, nouns, and adjectives must
not be discarded as being inferior to function lemmas in the
identification of authorship, since they provide valuable insights
to the Latinist on the individual differences in word usage by
the various authors.
The conclusion to be drawn from the differentiation between
the use of all most common lemmas and those lemmas with
the top 2 or 3 removed appears to be that a blind use of the
most frequent lemmas can skew the results, and demonstrates
that close cooperation between statistician and Latinist is
required.
The overall conclusion on the authorship attributions to Caesar
and Sallust are clear. The two works of Sallust appear to be
correctly attributed. The attributions to Caesar remain complex,
however: the text on the Spanish War is undeniably not that of
any literate Roman; and Gallic VIII and the Alexandrian War
appear definitely to be of separate authorship, and quite possibly
that of Hirtius, as the tradition claims. The most striking fact,
however, is that the first book on the Gallic Wars is of a high
literary quality, yet is undeniably different from the other works
of Caesar. Hence it now lies in the realm of the Latinist for a
full analysis of the author's uses of all parts of speech, and the
manner in which he apparently poured so much more effort
into this first book that brought his conquests in a new land to
the attention of the Roman People who would later be voting
on his bitterly fought candidature for the Consulship.
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