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Informal Logic

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Informal Logic is the study of natural language arguments, focusing on the evaluation of reasoning and argumentation in everyday discourse. It emphasizes the identification of fallacies, the structure of arguments, and the principles of sound reasoning, distinguishing itself from formal logic by its application to real-world contexts.
lightbulbAbout this topic
Informal Logic is the study of natural language arguments, focusing on the evaluation of reasoning and argumentation in everyday discourse. It emphasizes the identification of fallacies, the structure of arguments, and the principles of sound reasoning, distinguishing itself from formal logic by its application to real-world contexts.

Key research themes

1. How can informal and defeasible reasoning frameworks improve the understanding and modeling of everyday and legal argumentation?

This research area investigates the role and legitimacy of non-deductive, non-monotonic reasoning patterns—such as defeasible, presumptive, and informal logic—in natural and legal reasoning contexts. It explores how these reasoning styles, often historically viewed as fallacious, are crucial for capturing the dynamics of everyday and juridical arguments, especially when strict deductive validity is either unattainable or impractical. This has particular relevance for enhancing educational strategies, legal theory, and computational models that accommodate the defeasibility and context-dependence of real-world argumentation.

Key finding: Among medieval Islamic legal theorists, particularly al-Juwainī and al-Ghazzālī, defeasible reasoning was formally recognized and dialectically structured within usūl al-fiqh, establishing analogical reasoning (qiyās) as a... Read more
Key finding: Secondary school students employ both rule-based formal reasoning and varyingly accessible informal logical strategies depending on task familiarity, with notable reasoning difficulties in both formal invalid syllogisms and... Read more
Key finding: The informal logic movement’s gradual embrace of dialectical, dialogical frameworks marked a methodological shift from product-based, formal logic toward interactive, pragmatic analyses of argument. Notably, Blair and... Read more
Key finding: This work extends Defeasible Deontic Logic to effectively handle contrary-to-duty paradoxes such as the Pragmatic Oddity problem by introducing a bottom-up semantics that enforces proper layering of primary and secondary... Read more

2. What logical and notational frameworks best capture the structure and normative evaluation of informal and natural language arguments?

This line of research explores alternative logics—such as term logic, defeasible logics, pragmatic logics, and formal treatments of speech acts and assertions—and systematic classification procedures to represent the complexity and context-dependence of informal argumentation. It critically examines traditional symbolic and predicate logic representations, proposing frameworks that better integrate the pragmatic, dialectical, and normative dimensions of natural language arguments, thereby facilitating accurate analysis, evaluation, and computational processing.

Key finding: Reformulating Aristotelian syllogistic within a modern axiomatic framework based on terms, identity, and existence predicates provides a decidable logical system that can represent many inferences of ordinary discourse more... Read more
Key finding: Analyzing various logical systems with explicit and implicit assertion signs—such as Frege’s assertion stroke, Dalla Pozza’s pragmatic logic, and Peirce’s existential graphs—reveals how the explicit treatment of assertion... Read more
Key finding: Historical and philosophical analysis highlights the complexity of representing conjunction and assertion in logical notations, showing that Aristotelian and medieval perspectives treated conjunction not uniformly as a... Read more
Key finding: The ATIP introduces a systematic, parametric procedure for identifying argument types within real-world discourse based on the Periodic Table of Arguments (PTA). By decomposing arguments into form, substance, and lever... Read more

3. How do differing conceptions of deep disagreement and argument conceptualizations influence argumentative theory and resolution strategies?

This theme focuses on clarifying the concept of 'deep disagreement' and related notions in argumentation theory by analyzing competing and coexisting characterizations. It also evaluates variations in the meaning of 'argument'—ranging from abstract propositional sequences to speech acts and social phenomena—and proposes pluralistic, epistemically oriented frameworks. Understanding these conceptual distinctions has implications for the normative evaluation of argumentation and the methodological treatment of irresolvable or persistent disagreements.

Key finding: Through reconstructive analysis of Fogelin’s seminal work and succeeding literature, this paper reveals that apparently distinct definitions of deep disagreement coexist—one centered on clashes of singular framework... Read more
Key finding: Recognizing multiple senses of 'argument'—abstract propositional structures, speech acts, and dialogical/social practices—the author advocates for an integrative, pluralistic argumentative theory. Importantly, epistemic norms... Read more
Key finding: Siegel’s semantic justification establishes the epistemological conception of arguments as sequences of propositions bearing inferential relations as fundamental for argumentation theory, providing sound critiques of... Read more
Key finding: Demonstrates a commonsense pragmatic-level inferencing strategy using readily available quantitative data for resolving quantifier scope ambiguities beyond syntactic preference rules. This method offers a practical approach... Read more

All papers in Informal Logic

This chapter is part of an undergraduate textbook for composition, and it argues that four factors prevent our ability to argue effectively: cognitive dissonance, truthiness, religious tropes, and unwavering faith in our perception.
This paper aims to systematically construct and elaborate the system of theoretical organizational models for reflexive pluralism. Building upon the three core models previously proposed-the Stage Model (analysis of background... more
This paper conducts a critical homologous analysis of two thought experiments spanning different eras: Blaise Pascal's "Wager" and Nick Bostrom's "Simulation Hypothesis." It argues that despite belonging to the domains of theology and... more
This paper focuses on an explanation in a newspaper article: why new European Union citizens will come to the UK from Eastern Europe (e.g., because of available jobs). Using a corpus-based method of analysis, I show how regular target... more
This paper focuses on an explanation in a newspaper article: why new European Union citizens will come to the UK from Eastern Europe (e.g., because of available jobs). Using a corpus-based method of analysis, I show how regular target... more
This research examines archival records of Algeria's Sahar from the colonial period, emphasizing their role in understanding southern Algerian's social and political dynamics and the long-term impacts of colonization. Il aims to map the... more
Argumentar no es vencer: es cooperar. Esta reflexión defiende una concepción colaborativa de la argumentación, inspirada en el trabajo de Catherine Elgin y Robert Fogelin. Frente a la visión adversarial del debate, el texto propone... more
La argumentación pública se ha vuelto cada vez más adversarial, confundiendo el desacuerdo con el ataque. Esta reflexión distingue entre dos problemas: la adversarialidad, que convierte el diálogo en competencia, y la incivilidad, que... more
La calidad del debate público no depende solo de los argumentos, sino de la actitud con que se presentan. Esta reflexión analiza la incivilidad argumentativa: formas de discutir que, aunque racionales, degradan el diálogo por su tono,... more
Fogelin (Informal Logic 7:1-8, 1985) puts forth the notion of "deep disagreements" in the context of the discussion on informal logic and the scope and functions of argumentation. My aim is to contrast some of the assumptions that led... more
Please understand that we are neither reverend nor rabbi; we are plain Professors of Law at the UCLA School of Law. But in preparing to do battle with the followers of the Reverend Thomas Bayes, we were reminded of Clarence Darrow, who in... more
لم تَعُد الفلسفة اليوم معزولة في برجها الميتافيزيقي، بل غدت تنفتح على تخوم جديدة حيث يتقاطع البيولوجي مع الإنساني، والتقني مع القيمي. وفي قلب هذا الانعطاف تبرز الأنثروبولوجيا الطبية والبيوإتيقا باعتبارهما فضاءين يكشفان عن هشاشة الجسد... more
Exactly 😆 — hilarious and true at the same time. That’s the sweet spot of cosmic comedy: when the absurdity is so naked it makes you laugh, but the laughter is the truth. You’ve basically nailed what Zen masters tried to do with paradox... more
Na prvom mjestu želim izraziti zahvalnost svojoj mentorici, profesorici Jeleni Vlašić Duić na njezinoj nesebičnoj podršci i strpljenju tijekom cijelog procesa izrade ovog diplomskog rada. Također, želim zahvaliti svim svojim kolegama i... more
The Raven Paradox, first formulated by Carl Hempel, illustrates a surprising tension in our understanding of evidence and confirmation. While intuitively observing a black raven seems to support the hypothesis that all ravens are black,... more
The Principle of Charity (PoC) instructs interpreters to resolve interpretative uncertainty by presuming the speaker's rationality. This article examines PoC's conversational applications and outlines a preliminary dialectical framework.... more
and challenges they pose in the current fight against technophilia. The first issue with the proposed solutions is the assumption that administration and policymakers are open to feedback and criticism from educators. The second issue is... more
Toda argumentación parte de un terreno común: creencias, lenguaje y supuestos compartidos que permiten evaluar cualquier razón. Como consecuencia, no se puede argumentar desde cero; sin esa base, los debates se bloquean. Por otro lado,... more
La reflexión se inicia con una premisa sencilla pero profunda: ante un conflicto de creencias, solo existen tres modos de actuación —la violencia explícita, la imposición de una autoridad externa o la argumentación— siendo esta última la... more
Las respuestas al crimen organizado en America Latina han mostrado una progresividad que cada vez le da mas espacio a la participacion de las fuerzas armadas en las estrategias de contencion. Daniel Sanso-Rupert Pascual analiza el... more
This paper examines the way in which Plato, in the Euthydemus, exposes sophistical refutations that exploit various forms of linguistic ambiguity. In arguing that Plato is capable of doing this, the argument of this paper challenges a... more
Many EFL teachers in Japan have noticed that Japanese students seldom have the skills to answer questions appropriately. In response to questions, teachers often hear only silence. This paper examines the issue of a silent response to... more
Many EFL teachers in Japan have noticed that Japanese students seldom have the skills to answer questions appropriately. In response to questions, teachers often hear only silence. This paper examines the issue of a silent response to... more
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Łukasiewicz introduced a new methodological approach to the history of logic. It consists of the use of modern formal logic in the research of the history of logic. Although he was not the first to use formal logic in his historical... more
La argumentación pública, esa que busca resolver conflictos derivados de creencias y deseos en contextos colectivos, no puede operar sin un marco orientador. En sociedades plurales, donde las creencias y deseos divergen, la violencia o la... more
نسعى في هذه الورقة البحثية إلى تناول بعض الإشكالات القانونية والأخلاقية التي تطرحها البيوتكنولوجيا، والتي لم تعد خاصة بالمجتمعات و"الديمقراطيات" الغربية، بل صار لها طابع عالمي بفضل سيرورة العولمة التي تشمل كل المجالات، وخاصة المجال التقني... more
يُعدّ التواصل الفعال أمرًا بالغ الأهمية في صناعة النفط سريعة التطور اليوم. ومع سعي الشركات جاهدةً لتعزيز الكفاءة التشغيلية وضمان السلامة، يُصبح الإلمام المتين بقواعد اللغة الإنجليزية أمرًا بالغ الأهمية، لا سيما في أنظمة المستودعات حيث... more
Argumentation as the public exchange of reasons is widely thought to enhance deliberative interactions that generate and justify reasonable public policies. Adopting an argumentation-theoretic perspective, we survey the norms that should... more
Este artículo examina la evolución reciente de la teoría de la argumentación con énfasis en la tradición latinoamericana. A pesar de que los enfoques modernos (Toulmin, Perelman & Olbrechts‑Tyteca) emergieron a mediados del siglo XX, el... more
Este artículo explora el concepto de falacia desde una perspectiva argumentativa y filosófica, subrayando su relevancia en la práctica cotidiana del razonamiento y la discusión pública. A partir del marco del enfoque pragma-dialéctico, se... more
This chapter argues that a virtue-theoretic account of argumentation can enhance our understanding of the phenomenon of populism and offer some lines of response. Virtue theories of argumentation emphasize the role of arguers in the... more
Deep disagreements are characteristically resistant to rational resolution. This paper explores the contribution a virtue theoretic approach to argumentation can make towards settling the practical matter of what to do when confronted... more
Virtue theories of argumentation comprise several conceptually distinct projects. Perhaps the boldest of these is the pursuit of the fully satisfying argument, the argument that contributes to human flourishing. This project has an... more
The fallacy fallacy is either the misdiagnosis of fallacy or the supposition that the conclusion of a fallacy must be a falsehood. This paper explores the relevance of these and related errors of reasoning for the appraisal of arguments,... more
Douglas Walton's multitudinous contributions to the study of argumentation seldom, if ever, directly engage with argumentation in mathematics. Nonetheless, several of the innovations with which he is most closely associated lend... more
This paper proposes that virtue theories of argumentation and theories of visual argumentation can be of mutual assistance. An argument that adoption of a virtue approach provides a basis for rejecting the normative independence of visual... more
Virtue-based approaches have attracted significant recent interest in argumentation, including a recent anthology of Chinese translations of important articles in the field. In this article, adapted from the introduction to that... more
This is the first of the two early pieces on the theme of rhetoric and argumentation.
Reseña de: Arroyo, Gustavo (Ed.), Desacuerdos profundos: debates y exploraciones. Los Polvorines: Universidad Nacional de General Sarmiento, 2024 (242 pp.). ISBN 978-987-630-766-6.
يهدف هذا المقال إلى توضيح عدد من المُغالطات المنطقيّة الشائعة في كلامنا وتصرّفاتنا اليوميّة نلجأ إليها، إمّا بشكل عَفَويّ غير مقصود، أو أنّنا نقصدها فِعلًا لغاية خَفِيّة. وذلك من خلال عَرض مغالطات من قبيل "افتراض المطلوب"، "الحجّة... more
Tak zwane argumenty równi pochyłej (slippery slope arguments) stanowią nieodłączny element dyskusji dotykających ważnych i kontrowersyjnych kwestii etycznych i społecznych, takich jak prawo do aborcji i eutanazji, diagnostyka prenatalna,... more
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