Abstract
This paper surveys ontological modeling of rhetorical concepts, developed for use in argument mining and other applications of computational rhetoric, projecting their future directions. We include ontological models of argument schemes applying Rhetorical Structure Theory (RST); the RhetFig proposal for modeling; the related RetFig Ontology of Rhetorical Figures for Serbian (developed by two of the authors); and the Lassoing Rhetoric project (developed by another of the authors). The Lassoing Rhetoric venture is interesting for its multifaceted approach to linguistic devices, prominently including rhetorical figures, but also RST relations and stylistic models, like the use of historic present. This application takes a natural language text input and uses syntactic parsing tools to produce a knowledge base of linguistic entities using references to an OWL ontological framework, locating these devices using Semantic Web Rule Language (SWRL) logic rules. The paper also reports on a similar approach in research into detecting ironic tweets in a Serbian twitter corpus. The rhetorical schemes used for argument mining are also presented, as well as some suggestions for novel argument schemes based on the ontological approach to rhetorical figuration.
Introduction
Rhetorical figures from
Perelman and Olbrechts-Tyteca looked at rhetorical figures as argumentative, thus making a distinction between “an embellishment, a figure of style and argumentative figures, figures that potentially affect the audience’s rational perception of a standpoint” [53]. Figures are not considered as merely decorative but as a way to deal with the semantics of argumentative discourse. In their
Tindale wrote that rhetorical figures either constitute or emphasize arguments, arguing that
Fahnestock tells us figuration is part of the theory of argument. At least some figures epitomize arguments in their form. Thus, figures are seen as apt or epitomizing iconic forms for the arguments they express [19]. Taking into account the argumentative function of rhetorical figures, explored at length in the program of figural logic of Fahnestock [18], as well as in [61] and [30], we argue that inclusion of formal models of rhetorical figures in argument mining systems would enhance the performance of those systems. Different representations of rhetorical figure models might be utilized, some of which we present in this paper.
This paper also explores arguments from the standpoint of argument schemes and different approaches to their modeling. We take into account some overlapping terminology that appears both in Classical rhetoric tradition and in the Rhetorical Structure Theory practice. While some researchers rightly point out RST’s lack of connection to the rhetorical tradition, and the substantial difference between its coherence relations and rhetorical figures [58], we look at the real similarities between figures and coherence relations as fortuitous and discuss the ways in which they can be employed to enhance the existing argument mining systems, using our own approaches to knowledge engineering in the domain of rhetorical analysis which involve both knowledge modeling and reasoning systems.
The fields of Computational Linguistics and Natural Language Processing have “exploded in recent years” and provide “robust learning and processing systems applied to large corpora” [11]. In this domain, machine learning and stochastic approaches have become the main assets in default toolsets for analysing text, with significantly positive results. Ontological approaches we believe, however, can add value where statistical options cannot. Knowledge-based systems can be broadly divided into two areas: “Knowledge models – formalisms for knowledge representation and reasoning, and Reasoning systems – software that generates conclusions from available knowledge using logical techniques such as deduction and induction” [3]. Automatic detection of rhetorical figures in text and their annotation based on machine learning and ontological approaches has been explored for
We formalise the description of particular rhetorical domains which can aid argument mining efforts in two styles in this paper. The first is the
The remainder of the paper is organized as follows. Section 2 describes argument schemes and presents their various applications. Section 3 outlines the approaches to rhetorical figuration modeling which can be used for enhancement of argument mining systems. In Section 4, a composite figuration approach to argument mining is proposed and analyzed. Finally, Section 5 presents our future work and gives many concrete suggestions for future developments.
Argument schemes
Argument representations and rhetorical representations
Many forms of argument were identified and discussed by Aristotle.
Schemas in
While RST was developed almost wholly independently from the rhetorical tradition, there are some interesting overlaps. For instance, antithesis is both an RST relation, and a rhetorical figure (a trope), and the two are virtually isomorphic. Antithesis, as an RST relation, is of interest for argument studies which has contrast in positive regard at its core. Mann and Thompson [41] give its functional representation regarding N (nucleus), S (satellite) and their constraints. N and S are in contrast; because of the incompatibility that arises from the contrast, one cannot have positive regard for both of those situations. For example, N can contain an idea that is favored by the author, and S, on the other hand, can contain an idea that is disfavored by the author. Like antithesis the trope, Mann and Thompson’s relation is concerned with proximal opposing predictions. Treatments of figure, however, stress a wider range of functions. The RST relation is concerned primarily with quasi-logical and pragmatic relations, and its overall role in achieving text coherence, while the figural tradition stresses the creation of paradoxes, the generation of polarities and binaries in arguments, and the aesthetic function. We feel, however, that these are only differences of theoretical focus and that the relation and the figure are effectively interchangeable.
To summarize, the task of argument mining can be approached by using three types of schemes, the classical approach of using topoi, reimagined as argument schemes, the RST schemas and our goal here is to show that a third type of schemes,
Applications of argument schemes
Various applications have utilized the capability of RST to describe and help generate argumentative discourse. From a theoretical point of view Azar [2] investigates five RST relations (Evidence, Motivation, Justify, Antithesis, Concession) and their logical/pragmatic equivalents in the realm of arguments (supportive, incentive, justifier, persuader). Strategies for generating evaluative arguments (i.e., arguments that attempt to affect attitudes, as opposed to factual and casual arguments, which affect beliefs) are discussed in [7] and [8]. In [67] RST was used to model and analyze a corpus of argumentative discourse structures. Habernal, Eckle-Kohler and Gurevych [28] use a combined approach in which they build upon Walton’s argument schemes and combine them with the Claim–Premises scheme [52] and argue that an annotation scheme for argument mining is a function of the task requirements and the corpus properties. Green [24] developed a hybrid argument presentation scheme for biomedical research that enables an analyst to encode argument analysis within the RST framework, which can be used to represent the discourse structure of a text.
Many of the most common and important schemes have been identified and analyzed by [33,53,55,66] and [65]. For argument mining purposes, each scheme is associated with a set of identifiers (key words and markers locating premises and conclusions), and when the right grouping of identifiers is located at some place in a text, the argument mining method locates it as an instance of an argument of some particular, identifiable type (from a list of schemes) as shown in [66]. This approach was used for argument mining with argument scheme structures in [39] and it was the basis of the ontological approach to modeling arguments on the Web, as shown in [4].
Jeanne Fahnestock’s work exploring rhetorical figures in scientific arguments [18] has laid a foundation for looking into rhetorical and argumentative structures in highly technical, precise, and rigorous arguments. Similarly, some of the most prominent discourse representation models focusing on arguments at the intersection of RST and ontological modeling were developed with the goal of analyzing highly technical, precise, and rigorous publications. Many of these approaches have used Semantic Web standards as the data representation model for arguments. Examples include ScholOnto [6], works presented in [14] and [45], AIF and SALT.
ScholOnto (The Scholarly Ontologies project) is based on the decomposition of a scientific publication into elementary discourse knowledge items and their connection via a set of relations. The authors provide a relatively simple set of argument links to make it as easy as possible to add an argument link to a concept or claim. The discourse representation model proposed by de Waard and Tel [14] has an arrangement they call
The AIF (Argument Interchange Format) is a core ontology of argument-related concepts which can be extended to capture a variety of argument formalisms and argument schemes. The argument schemes can be classified further into: rule of inference scheme, conflict scheme, preference scheme, etc. AIF was first introduced in [10]. The original AIF ontology had two disjoint types of nodes: information nodes and scheme nodes. Information nodes are used to represent passive information contained in an argument, such as a claim and premise, while scheme nodes capture the application of schemes (i.e., patterns of reasoning). The AIF description is available as a number of different specifications in different languages (such as OWL-DL, RDF-S and SQL).

SALT Rhetorical Ontology Layer (adapted from [25]).
The SALT Framework (Semantically Annotated LaTeX) [26] is a semantic authoring framework targeting the enrichment of scientific publications with semantic metadata. SALT adopts RST elements and models discourse knowledge items and their intrinsic coherence relations. The framework comprises three ontologies: the Document Ontology, the Rhetorical RST Ontology and the Annotation Ontology that connects the rhetorical structure present within the document’s content to the actual content of the document. Applying SALT on a scientific publication leads to a local instance model capturing the inter-connected linear, rhetorical and argument structures within that publication.
The Rhetorical RST Ontology layer of this framework consists of three major sides, as diagrammed in Fig. 1: (i) coherence relations side that models elements (e.g., claims or supports) and the relations connecting them (e.g., Antithesis, Circumstance, Concession or Purpose); (ii) rhetorical blocks side that provides a coarse-grained structure for modeling the discourse (e.g., abstract, motivation, background or conclusion); (iii) argument side that captures the argument present in the publication via concepts like Issue, Position or Argument. This Rhetorical layer can be enriched with ontologically modeled separate rhetorical figures to enable fine-grained annotations of rhetorical figures which play an important part in arguments, following approaches to figurational modeling used in [22,32] and [58], as well as our approach to modeling rhetorical figures, as described in Section 3.2 of this paper.
Introduction
The discipline of ontological engineering defines many different approaches to conceptualizing a domain. A large body of ontologies are now utilising OWL1
OWL is not the only suitable ontological framework for modeling natural language. In our research so far, only occasional workarounds have been needed to manage any inadequacies with practical implementations. However, the investigation of alternatives [36] should be within the scope of all projects that utilize techniques of ontological engineering.
Semantic Web Rule Language (SWRL) rules are Description Logic-based sets of terms that allow logical inference across a knowledge base. SWRL can also be understood as an extension to OWL which provides an efficient way for representing statements that are not expressed by an ontology itself but inferred from them. For example, from the following SWRL rule it can be inferred who is a parent – “a person who has at least one child”.
Ontologies outlined in this paper are designed partly from a
The Semantic Web approach to developing a semantic network of readily-comparable and translatable data is still in its relative infancy, but has been growing more quickly in recent years [17]. This movement has opened the door to academic projects that seek to benefit from this approach and interoperability.
Two models of using ontological knowledge, and inferred knowledge based on the rules, in order to detect rhetorical figures in texts in a natural language are presented in the next two subsections. The first of them describes using a formal domain ontology of rhetorical figures for Serbian (The
A formal domain ontology of rhetorical figures for Serbian (The
Taking into account that a rhetorical figure is a fundamentally linguistic phenomenon, in the
A method of detection of rhetorical figures in the Serbian language, specifically While the Waterloo Taxonomy of Rhetorical Figures (utilized by the glossary provided in the introduction) treats irony as chroma [31], RetFig follows the more traditional classification of irony as a trope.
A tool which uses one SWRL rule to infer if a linguistic structure extracted from a text belonging to the collection of texts in Serbian (consisting of 10 digitized writings of various genres – children‘s songs, fairy tales, comedies, novels and essays) represents the figure
With the help of antonymous pairs, the real meaning of an ironic tweet can be comprehended, as in the following example: “O, baš sam srećan što je Dr Igi najavio svoj povratak!” (O, how happy I am to see Dr Iggy’s comeback!) where in the SWN ontology there are: a direct antonymous pair (happy – unhappy), eight indirect antonymous pairs inferred by SWRL rule
The tweet can therefore be interpreted with an opposite of the intended meaning: “O, how cheerless I am to see Dr Iggy’s comeback!” or any one of the adjectives opposite to the adjective “happy” from the third column of the Table 1 can be used. As it was mentioned above, inferred examples of
Datatype properties of the SWN ontology classes
The rhetorical figure
The
An approach that attempts to infer the location and structure of rhetorical devices was developed for the
To be able to structure the required elements in the knowledge base, a suite of ontologies was created. Separating OWL ontology URIs in this way allows for greater flexibility and more specific re-use across the Semantic Web. This design choice benefits users of the online resources and is an important paradigm of the Semantic Web project.
Pre-processing of the text data consists of a standard parsing routine (using GATE9
The GATE processing output, including the Stanford Parser – gate.owl12
Linguistic entities and relationships – langtag.owl13
Document structure, language/text entities and relationships – DocStruct.owl14
External entities and relationships and associated intra-ontology relationships – VerbNounCombo.owl
Rhetorical devices, figures of speech and RST coherence relations – RhetoricalDevices.owl
The project ontology – LassoingRhetoric.owl
The knowledge base contains the various instantiated classes that relate to, firstly, linguistic entities: words, punctuation, sentence, etc. (
Many rhetorical figures are structured around surface-level cues such as repeating phrases or token positioning. This is intuitively processed by a human reader without regard, but must be specified if a logic rule is to be used to infer anything on this basis. The Document Structure ontology (

Document Structure ontology class diagram.
Two other ontologies in the suite are used to specify more complex structures and rhetorical patterns by name. The
The Rhetorical Devices ontology15
Lastly, each of the ontologies in the suite are imported, via OWL syntax, into a project-level ontology.16
An example of a rule designed to discover a figure defined perhaps more readily by surface cues, is the rule for
This is a simplified version of a rule that could be very much more complex if we wanted to capture further examples of the figure. In order to capture more examples of
Strictly not a rhetorical figure and perhaps best considered a
Even though
This SWRL set of terms is acting as a production rule, which indicates that the output is the generation of a new set of RDF triples into the same knowledge base that describes the document. In this example, if all the various terms in the body of the rule are held true, then it is logically asserted that the head is held true also and therefore that the text document has an example of
The initial
An important part of the output of the design is the HTML viewer. This approach to visualisation is similar to others in the field, e.g., Michael Ullyot in his blog,17
http://ullyot.ucalgaryblogs.ca/2015/05/31/augmented-criticism-and-rhetorical-figures/
As well as the HTML output, a textual report of the elements calculated via the various processes is also generated. This is important to allow external scrutiny of the process involved in calculating the various elements in the text and the logical processes undertaken to reach the output. And further, a percentage figure is calculated to indicate how “rhetorical” the text is. This is obviously a very subjective score and only simplistically calculated as a ratio of the phrases containing rhetorical forms discovered by the rule system to those phrases not containing figures. Similar work in this area has been conducted on the Faciloscope Project.18

Lassoing Rhetoric – HTML output example.
Summarisation and quantification will, we believe, become an important feature of the field of computational rhetoric in the future. The desire to understand the overall form of an author’s persuasive intent is palpable in both rhetorician and non-rhetorician alike. The level at which quantification can be applied varies across a document and even to individual figures or types of figures. Chiastic figures (that is, figures of the Chiastic Suite, as defined in the glossary appended to the introduction of this issue) are those which have a criss cross nature at, for example, lexical level. Dubremetz and Nivre [15,16] analysed chiastic figures in terms of the extent to which they vary across this general prototypical form. By ranking the inverse lexical repetition configurations they were able to show quantified variation of
This type-ranking process of quantification naturally leads to further understanding of the prototypes and components of a figure such as
The
Since the structure of the project allows for complete contrivance towards the goal, i.e., a rule can be defined in advance and subsequently the ontological structure put in place along with the computational discovery logic to populate the knowledge base, it is likely that more complex rhetorical forms can be processed and located in text. The possibilities are huge compared with other techniques where complex logical structures have to be interpreted or learned, for example, in machine learning algorithms. This is an area for future development.
The potential benefits of this system to general knowledge cannot be understated. It is possible to create semantically-tagged representations of any textual work (where language parsers exist) that relate to a growing, coherent set of concepts and world knowledge data. The uses for this approach, from corpus analysis to rhetorical figuration scholarship, are not yet fully investigated.
It is recognised that the Semantic Web movement hasn’t yet fully realised the potential that was originally promised. Many of the reasons for this were predicted, however the progress is still moving forward and it is hoped that a semantically rich network of data will soon start to make more sense as a real prospect. In the meantime, the proof of concept
Argument models differ in granularity, expressive power, and other properties. Because of the lack of a single general-purpose argument model there is a need for using different schemes for different scenarios. [56] has shown that many schemes are structurally related in an interesting way – many of the most common schemes have an interlocking relationship with other schemes so that one scheme can be classified as a subspecies of another, but only in a complex manner. Building a robust model for argument mining based on combining different approaches to acquiring computational understanding of the way arguments work is a goal which can, in part, be achieved by combining different methods for designing the building blocks of the arguments themselves. Adding rhetorical figures to these models would increase granularity and leverage two and half millennia of formal study, because the arguments drawn from the figures according to [61], engage the audience at a deep, often emotional level, before reason moves in as an organizing force. Thus, formal models of rhetorical figures used for enhancing argument mining systems are expected to bring better results in performance of these systems.
Composite effects of rhetorical figures have always been known in terms of an increased aesthetic appeal in some configurations. New areas of rhetorical research are being discovered now, almost three millennia into the scholarship on figures. Composite figuration makes detection more reliable and constrains functions and is therefore a boon to argument mining and other computational-textual activities [31,58]. “And so, my fellow Americans: ask not what your country can do for you – ask what you can do for your country.”
This famous statement uttered during the inaugural speech address of the 35th president of the United States of America, John F. Kennedy, can be seen as an argument scheme of its own, in the ontological rhetoric modeling sense. It is considered as a highly persuasive statement. It contains three distinct rhetorical figures: the whole statement is an
Still, detecting composite rhetorical devices such as these is indispensable and can lead to a better understanding of the way arguments are formed, which can secure a more straightforward machine analysis and understanding of those arguments. Ruan et al. [58] analyze this famous sentence and argue that is is so widely known and frequently invoked because of the “schematic congruence with which the form matches the Reject–Replace function its arrangement serves” and because of the cognitive affinities humans have for the structural properties of this kind of figural stacking – opposition, repetition, and symmetry. The same authors also point out that this kind of statement is especially interesting because of its form-functional correlation, stemming from the program of figural logic of Jeanne Fahnestock. Thus, the form of this famous Kennedy’s statement (written by his speech writer, Ted Sorensen) makes it tractable for automated detection, while the function accounts for its rhetorical purpose. Detection of composite rhetorical figures which appear in the statement itself can be achieved following the ontological modeling approach presented in Sections 3.2 and 3.3.
Imagining further the nature of mixtures of rhetorical figures (which is surely what most documents are), we foresee a fruitful effort in combining analytical and statistical ranking methods [15] with a larger-document approach [51] and an approach to annotating stacks of figures proposed in [58]. Under such scrutiny, we predict that the models we have for figures will uncover a greater complexity of foundational constituents (such as parallelism and symmetry) and complementary elements (such as semantic and pragmatic augmentation) that brings insights into the cognitive basis for understanding. Another interesting approach by Mehlenbacher [44] proposes that
Future work
We summarise four areas of future development:
Broadening of logic rules
In this paper we showed that semantic knowledge of domain ontologies like the
Publishing online and defining standards
Several projects were reported in this paper, each taking a slightly different approach. These applications discover rhetorical forms from natural language and by using OWL ontologies and SWRL rules, are able to extend the work by publishing the results to the internet and, in tandem, the ontological framework and SWRL rules. Ultimately this allows for unprecedented sharing and collaboration. Other projects in this field we recognise are Ruan et al. [58] and ROAP.19
A specific problem to be addressed in the near future is agreeing to a standard for ontological approaches in this domain. There are a number of groups working on ontologies of rhetorical figures that have many shared concepts [58]. These concepts have been modeled in different ways, depending on the application or language within which the work is undertaken, but a translation mechanism and set of agreements would be beneficial. Defining, publishing and sharing these common elements is essential while these projects remain relatively young. Once knowledge bases of meaning representations for specific texts are published online, there is also a need to define these in a form that is re-usable by others in this or associated fields. For example, marked-up corpora that describe a text would be more useful if they were in a standard and recognised format. There is a wealth of public domain and research-friendly text resources available. The project aimed at parsing these documents and processing them into re-usable knowledge bases would be useful for many others.
A number of challenges are becoming more clear as work in this field develops, especially around the writing of logic rules and ontology design. Utilising statistical techniques in tandem with ontological and inferential ones, we would expect improvements in effectiveness. A future area for investigation would therefore be machine learning augmentation of ontological approaches. This is a huge area for investigation, but some specific examples are:
executing a supervised learning algorithm on a corpus of known figures to produce probabilistic models of key terms that can be used in logic rules
developing inter-inference filters that operate alternatively and in tandem with an inferential approach, e.g., between iterative applications of rule-based logical inferences each rule set is augmented by the results of probabilistic models
executing a clustering algorithm over a text to highlight rudimentary terms to be collated into rule sets
An even more challenging area of investigation is pragmatic augmentation. Many facets of understanding rely on contextual knowledge. Therefore increasing the quantity and scope of world knowledge injection into rules and knowledge bases is an area that would also be fruitful. The Linked Data movement has grown considerably in the last five years and it is growing ever plausible to create useful links across data sets.
Potential applications
As discussed earlier in this paper, there are numerous and potentially fruitful areas to investigate regarding quantification of rhetorical figures at various levels. The hypothesis that an author has a distinct profile of quantified figures is one that could also be very useful, especially for the following ideas for applications:
author recognition and discovery
plagiarism detection
comparing authors and speech-writers
political discourse analysis
argument/intent analysis, e.g., hate speech detection
The rudimentary score developed in the
As we mentioned previously in this paper, we hope that further analysis of rhetorical figures will reveal a deeper understanding of the cognitive aspects that underlie the impact of persuasive communication. A conjunction of domains such as psychology, cognitive science, philosophy, computer science and rhetoric provides a rewarding furrow to plough.
Footnotes
Acknowledgement
A series of workshops on Computational Rhetoric held at the University of Waterloo strive to bring together researchers from the fields of Rhetoric, Computer Science, Linguistics, Cybernetics, Information Science, Literary studies, Psychology and Philology. This paper was inspired by the presentations and rich discussions experienced at the last Computational Rhetoric workshop of the University of Waterloo, held in August 2016.
