Ryuta Arisaka

Ryuta Arisaka, Ryoma Nakai, Yusuke Kawamoto et al.

From daily discussions to marketing ads to political statements, information manipulation is rife. It is increasingly more important that we have the right set of tools to defend ourselves from manipulative rhetoric, or fallacies. Suitable techniques to automatically identify fallacies are being investigated in natural language processing research. However, a fallacy in one context may not be a fallacy in another context, so there is also a need to explain how and why it has come to be judged a fallacy. For the explainable fallacy identification, we present a novel approach to characterising fallacies through formal constraints, as a viable alternative to more traditional fallacy classifications by informal criteria. To achieve this objective, we introduce a novel context-aware argumentation model, the theme aspect argumentation model, which can do both: the modelling of a given argumentation as it is expressed (rhetorical modelling); and a deeper semantic analysis of the rhetorical argumentation model. By identifying fallacies with formal constraints, it becomes possible to tell whether a fallacy lurks in the modelled rhetoric with a formal rigour. We present core formal constraints for the theme aspect argumentation model and then more formal constraints that improve its fallacy identification capability. We show and prove the consequences of these formal constraints. We then analyse the computational complexities of deciding the satisfiability of the constraints.

Ryuta Arisaka

We make three contributions. First, we formulate a discussion-graph semantics for first-order logic with equality, enabling reasoning about discussion and argumentation in AI more generally than before. This addresses the current lack of a formal reasoning framework capable of handling diverse discussion and argumentation models. Second, we generalise Dung's notion of extensions to cases where two or more graph nodes in an argumentation framework are equivalent. Third, we connect these two contributions by showing that the generalised extensions are first-order characterisable within the proposed discussion-graph semantics. Propositional characterisability of all Dung's extensions is an immediate consequence. We furthermore show that the set of all generalised extensions (acceptability semantics), too, are first-order characterisable. Propositional characterisability of all Dung's acceptability semantics is an immediate consequence.

Ryuta Arisaka, Takayuki Ito

In this paper, we propose a fresh perspective on argumentation semantics, to view them as a relational database. It offers encapsulation of the underlying argumentation graph, and allows us to understand argumentation semantics under a single, relational perspective, leading to the concept of relational argumentation semantics. This is a direction to understand argumentation semantics through a common formal language. We show that many existing semantics such as explanation semantics, multi-agent semantics, and more typical semantics, that have been proposed for specific purposes, are understood in the relational perspective.

Ryuta Arisaka, Takayuki Ito

Labelling-based formal argumentation relies on labelling functions that typically assign one of 3 labels to indicate either acceptance, rejection, or else undecided-to-be-either, to each argument. While a classical labelling-based approach applies globally uniform conditions as to how an argument is to be labelled, they can be determined more locally per argument. Abstract dialectical frameworks (ADF) is a well-known argumentation formalism that belongs to this category, offering a greater labelling flexibility. As the size of an argumentation increases in the numbers of arguments and argument-to-argument relations, however, it becomes increasingly more costly to check whether a labelling function satisfies those local conditions or even whether the conditions are as per the intention of those who had specified them. Some compromise is thus required for reasoning about a larger argumentation. In this context, there is a more recently proposed formalism of may-must argumentation (MMA) that enforces still local but more abstract labelling conditions. We identify how they link to each other in this work. We prove that there is a Galois connection between them, in which ADF is a concretisation of MMA and MMA is an abstraction of ADF. We explore the consequence of abstract interpretation at play in formal argumentation, demonstrating a sound reasoning about the judgement of acceptability/rejectability in ADF from within MMA. As far as we are aware, there is seldom any work that incorporates abstract interpretation into formal argumentation in the literature, and, in the stated context, this work is the first to demonstrate its use and relevance.

Ryuta Arisaka, Takayuki Ito

A negotiation process by 2 agents e1 and e2 can be interleaved by another negotiation process between, say, e1 and e3. The interleaving may alter the resource allocation assumed at the inception of the first negotiation process. Existing proposals for argumentation-based negotiations have focused primarily on two-agent bilateral negotiations, but scarcely on the concurrency of multi-agent negotiations. To fill the gap, we present a novel argumentation theory, basing its development on abstract persuasion argumentation (which is an abstract argumentation formalism with a dynamic relation). Incorporating into it numerical information and a mechanism of handshakes among members of the dynamic relation, we show that the extended theory adapts well to concurrent multi-agent negotiations over scarce resources.

Ryuta Arisaka, Takayuki Ito

The semantics as to which set of arguments in a given argumentation graph may be acceptable (acceptability semantics) can be characterised in a few different ways. Among them, labelling-based approach allows for concise and flexible determination of acceptability statuses of arguments through assignment of a label indicating acceptance, rejection, or undecided to each argument. In this work, we contemplate a way of broadening it by accommodating may- and must- conditions for an argument to be accepted or rejected, as determined by the number(s) of rejected and accepted attacking arguments. We show that the broadened label-based semantics can be used to express more mild indeterminacy than inconsistency for acceptability judgement when, for example, it may be the case that an argument is accepted and when it may also be the case that it is rejected. We identify that finding which conditions a labelling satisfies for every argument can be an undecidable problem, which has an unfavourable implication to existence of a semantics. We propose to address this problem by enforcing a labelling to maximally respect the conditions, while keeping the rest that would necessarily cause non-termination labelled undecided. Several semantics will be presented and the relation among them will be noted. Towards the end, we will touch upon possible research directions that can be pursued further.

Ryuta Arisaka, Makoto Hagiwara, Takayuki Ito

From marketing to politics, exploitation of incomplete information through selective communication of arguments is ubiquitous. In this work, we focus on development of an argumentation-theoretic model for manipulable multi-agent argumentation, where each agent may transmit deceptive information to others for tactical motives. In particular, we study characterisation of epistemic states, and their roles in deception/honesty detection and (mis)trust-building. To this end, we propose the use of intra-agent preferences to handle deception/honesty detection and inter-agent preferences to determine which agent(s) to believe in more. We show how deception/honesty in an argumentation of an agent, if detected, would alter the agent's perceived trustworthiness, and how that may affect their judgement as to which arguments should be acceptable.

Ryuta Arisaka

Abstract Persuasion Argumentation (APA) is a dynamic argumentation formalism that extends Dung argumentation with persuasion relations. In this work, we show through two-counter Minsky machine encoding that APA dynamics is Turing-complete.

Ryuta Arisaka, Stefano Bistarelli, Francesco Santini

We contemplate a higher-level bipolar abstract argumentation for non-elementary arguments such as: X argues against Ys sincerity with the fact that Y has presented his argument to draw a conclusion C, by omitting other facts which would not have validated C. Argumentation involving such arguments requires us to potentially consider an argument as a coherent block of argumentation, i.e. an argument may itself be an argumentation. In this work, we formulate block argumentation as a specific instance of Dung-style bipolar abstract argumentation with the dual nature of arguments. We consider internal consistency of an argument(ation) under a set of constraints, of graphical (syntactic) and of semantic nature, and formulate acceptability semantics in relation to them. We discover that classical acceptability semantics do not in general hold good with the constraints. In particular, acceptability of unattacked arguments is not always warranted. Further, there may not be a unique minimal member in complete semantics, thus sceptic (grounded) semantics may not be its subset. To retain set-theoretically minimal semantics as a subset of complete semantics, we define semi-grounded semantics. Through comparisons, we show how the concept of block argumentation may further generalise structured argumentation.

Ryuta Arisaka, Jeremie Dauphin

Cycles of attacking arguments pose non-trivial issues in Dung style argumentation theory, apparent behavioural difference between odd and even length cycles being a notable one. While a few methods were proposed for treating them, to - in particular - enable selection of acceptable arguments in an odd-length cycle when Dung semantics could select none, so far the issues have been observed from a purely argument-graph-theoretic perspective. Per contra, we consider argument graphs together with a certain lattice like semantic structure over arguments e.g. ontology. As we show, the semantic-argumentgraphic hybrid theory allows us to apply abstract interpretation, a widely known methodology in static program analysis, to formal argumentation. With this, even where no arguments in a cycle could be selected sensibly, we could say more about arguments acceptability of an argument framework that contains it. In a certain sense, we can verify Dung extensions with respect to a semantic structure in this hybrid theory, to consolidate our confidence in their suitability. By defining the theory, and by making comparisons to existing approaches, we ultimately discover that whether Dung semantics, or an alternative semantics such as cf2, is adequate or problematic depends not just on an argument graph but also on the semantic relation among the arguments in the graph.

Ryuta Arisaka, Ken Satoh

The act of persuasion, a key component in rhetoric argumentation, may be viewed as a dynamics modifier. We extend Dung's frameworks with acts of persuasion among agents, and consider interactions among attack, persuasion and defence that have been largely unheeded so far. We characterise basic notions of admissibilities in this framework, and show a way of enriching them through, effectively, CTL (computation tree logic) encoding, which also permits importation of the theoretical results known to the logic into our argumentation frameworks. Our aim is to complement the growing interest in coordination of static and dynamic argumentation.

Ryuta Arisaka, Ken Satoh

We consider abstract-argumentation-theoretic coalition formability in this work. Taking a model from political alliance among political parties, we will contemplate profitability, and then formability, of a coalition. As is commonly understood, a group forms a coalition with another group for a greater good, the goodness measured against some criteria. As is also commonly understood, however, a coalition may deliver benefits to a group X at the sacrifice of something that X was able to do before coalition formation, which X may be no longer able to do under the coalition. Use of the typical conflict-free sets of arguments is not very fitting for accommodating this aspect of coalition, which prompts us to turn to a weaker notion, conflict-eliminability, as a property that a set of arguments should primarily satisfy. We require numerical quantification of attack strengths as well as of argument strengths for its characterisation. We will first analyse semantics of profitability of a given conflict-eliminable set forming a coalition with another conflict-eliminable set, and will then provide four coalition formability semantics, each of which formalises certain utility postulate(s) taking the coalition profitability into account.

Ryuta Arisaka

There are several major proposals for treating donkey anaphora such as discourse representation theory and the likes, or E-Type theories and the likes. Every one of them works well for a set of specific examples that they use to demonstrate validity of their approaches. As I show in this paper, however, they are not very generalisable and do not account for essentially the same problem that they remedy when it manifests in other examples. I propose another logical approach. I develoop logic that extends a recent, propositional gradual logic, and show that it can treat donkey anaphora generally. I also identify and address a problem around the modern convention on existential import. Furthermore, I show that Aristotle's syllogisms and conversion are realisable in this logic.

Ryuta Arisaka

The AGM recovery postulate says: assume a set of propositions X; assume that it is consistent and that it is closed under logical consequences; remove a belief P from the set minimally, but make sure that the resultant set is again some set of propositions X' which is closed under the logical consequences; now add P again and close the set under the logical consequences; and we should get a set of propositions that contains all the propositions that were in X. This postulate has since met objections; many have observed that it could bear counter-intuitive results. Nevertheless, the attempts that have been made so far to amend it either recovered the postulate in full, had to relinquish the assumption of the logical closure altogether, or else had to introduce fresh controversies of their own. We provide a solution to the recovery paradox in this work. Our theoretical basis is the recently proposed belief theory with latent beliefs (simply the latent belief theory for short). Firstly, through examples, we will illustrate that the vanilla latent belief theory can be made more expressive. We will identify that a latent belief, when it becomes visible, may remain visible only while the beliefs that triggered it into the agent's consciousness are in the agent's belief set. In order that such situations can be also handled, we will enrich the latent belief theory with belief dependencies among attributive beliefs, recording the information as to which belief is supported of its existence by which beliefs. We will show that the enriched latent belief theory does not possess the recovery property. The closure by logical consequences is maintained in the theory, however. Hence it serves as a solution to the open problem in the belief set theories.

Ryuta Arisaka

In the classic AGM belief revision theory, beliefs are static and do not change their own shape. For instance, if p is accepted by a rational agent, it will remain p to the agent. But such rarely happens to us. Often, when we accept some information p, what is actually accepted is not the whole p, but only a portion of it; not necessarily because we select the portion but because p must be perceived. Only the perceived p is accepted; and the perception is subject to what we already believe (know). What may, however, happen to the rest of p that initially escaped our attention? In this work we argue that the invisible part is also accepted to the agent, if only unconsciously. Hence some parts of p are accepted as visible, while some other parts as latent, beliefs. The division is not static. As the set of beliefs changes, what were hidden may become visible. We present a perception-based belief theory that incorporates latent beliefs.

Ryuta Arisaka

Our understanding about things is conceptual. By stating that we reason about objects, it is in fact not the objects but concepts referring to them that we manipulate. Now, so long just as we acknowledge infinitely extending notions such as space, time, size, colour, etc, - in short, any reasonable quality - into which an object is subjected, it becomes infeasible to affirm atomicity in the concept referring to the object. However, formal/symbolic logics typically presume atomic entities upon which other expressions are built. Can we reflect our intuition about the concept onto formal/symbolic logics at all? I assure that we can, but the usual perspective about the atomicity needs inspected. In this work, I present gradual logic which materialises the observation that we cannot tell apart whether a so-regarded atomic entity is atomic or is just atomic enough not to be considered non-atomic. The motivation is to capture certain phenomena that naturally occur around concepts with attributes, including presupposition and contraries. I present logical particulars of the logic, which is then mapped onto formal semantics. Two linguistically interesting semantics will be considered. Decidability is shown.

Ryuta Arisaka

There is knowledge. There is belief. And there is tacit agreement.' 'We may talk about objects. We may talk about attributes of the objects. Or we may talk both about objects and their attributes.' This work inspects tacit agreements on assumptions about the relation between objects and their attributes, and studies a way of expressing them, presenting as the result what we term gradual logic in which the sense of truth gradually shifts. It extends classical logic instances with a new logical connective capturing the object-attribute relation. A formal semantics is presented. Decidability is proved. Para- consistent/epistemic/conditional/intensional/description/combined logics are compared.