This paper makes a case for a refined look at the so- called ‘fallacy of hasty generalization’ by arguing that this expression is an umbrella term for two fallacies already distinguished by Aristotle. One is the fallacy of generalizing in an inappropriate way from a particular instance to a universal generalization containing a ‘for all x’ quantification. The other is the secundum quid (‘in a certain respect’) fallacy of moving to a conclusion that is supposed to be a universal generalization (...) containing a ‘for all x‘ quantification while overlooking qualifications that have to be added to the more limited kind of generalization expressed in the premise. It is shown that these two fallacies relate to two different kinds of generalization. (shrink)

The work of Hugh MacColl (1837–1909) suffered the same fate after his death as before it:despite being vaguely alluded to and in part even commended, on the whole it has remained an unknown quantity. Even worse, those of his ideas which have played a decisive role in the history of logic have been credited to his successors; this is especially the case with the definition of strict implication and the first formal development of formal modal logic. This paper takes an (...) initial step towards a rectification of this unfortunate misrepresentation, presenting a bibliography of MacColl’s most significant publications with particular regard to their reception. (shrink)

Zoologist A. J. Cain began historical research on Linnaeus in 1956 in connection with his dissatisfaction over the standard taxonomic hierarchy and the rules of binomial nomenclature. His famous 1958 paper ‘Logic and Memory in Linnaeus's System of Taxonomy’ argues that Linnaeus was following Aristotle's method of logical division without appreciating that it properly applies only to ‘analysed entities’ such as geometric figures whose essential nature is already fully known. The essence of living things being unanalysed, there is no basis (...) on which to choose the right characters to define a genus nor on which to differentiate species. Yet Cain's understanding of Aristotle, which depended on a 1916 text by H. W. B. Joseph, was fatally flawed. In the 1990s Cain devoted himself to further historical study and softened his verdict on Linnaeus, praising his empiricism. The idea that Linnaeus was applying an ancient and inappropriate method cries out for fresh study and revision. (shrink)

This paper discusses the fallacies of combination and division as they are presented by Aristotle in chapter 4 of his Sophistici Elenchi. Aristotle's examples are concise, their discussion is unclear, and it is difficult to distinguish the cases of combination from those of division. I analyse the Aristotelian examples and the interpretations offered so far. I show that these interpretations suffer from a major defect: they fail to identify a common characteristic whereby the Aristotelian examples can be classified as instances (...) of combination or division. In my reconstruction of the examples, I repair this deficiency: I give a single pattern of explanation for the fallacy of combination and another (similar) pattern for the fallacy of division. Thus, it is possible to free Aristotle from the following charges: (i) he did not clearly distinguish between combination and division, and (ii) he reduced combination and division to a single fallacy. My explanation of the fallacies uses the notion of scope of an expression: in modern terminology, the fallacy of combination can be described as ?fallacy of the wide scope?, the fallacy of division as ?fallacy of the narrow scope? (shrink)

This paper argues that some traditional fallacies should be considered as reasonable arguments when used as part of a properly conducted dialog. It is shown that argumentation schemes, formal dialog models, and profiles of dialog are useful tools for studying properties of defeasible reasoning and fallacies. It is explained how defeasible reasoning of the most common sort can deteriorate into fallacious argumentation in some instances. Conditions are formulated that can be used as normative tools to judge whether a given defeasible (...) argument is fallacious or not. It is shown that three leading violations of proper dialog standards for defeasible reasoning necessary to see how fallacies work are: (a) improper failure to retract a commitment, (b) failure of openness to defeat, and (c) illicit reversal of burden of proof. (shrink)

This entry traces the historical development of the Square of Opposition, a collection of logical relationships traditionally embodied in a square diagram. This body of doctrine provided a foundation for work in logic for over two millenia. For most of this history, logicians assumed that negative particular propositions ("Some S is not P") are vacuously true if their subjects are empty. This validates the logical laws embodied in the diagram, and preserves the doctrine against modern criticisms. Certain additional principles ("contraposition" (...) and "obversion") were sometimes adopted along with the Square, and they genuinely yielded inconsistency. By the nineteenth century an inconsistent set of doctrines was widely adopted. Strawson's 1952 attempt to rehabilitate the Square does not apply to the traditional doctrine; it does salvage the nineteenth century version but at the cost of yielding inferences that lead from truth to falsity when strung together. (shrink)

My purpose in this chapter is to survey some of the principal approaches to inductive inference in the philosophy of science literature. My first concern will be the general principles that underlie the many accounts of induction in this literature. When these accounts are considered in isolation, as is more commonly the case, it is easy to overlook that virtually all accounts depend on one of very few basic principles and that the proliferation of accounts can be understood as efforts (...) to ameliorate the weaknesses of those few principles. In the earlier sections, I will lay out three inductive principles and the families of accounts of induction they engender. In later sections I will review standard problems in the philosophical literature that have supported some pessimism about induction and suggest that their import has been greatly overrated. In the final sections I will return to the proliferation of accounts of induction that frustrates efforts at a final codification. I will suggest that this proliferation appears troublesome only as long as we expect inductive inference to be subsumed under a single formal theory. If we adopt a material theory of induction in which individual inductions are licensed by particular facts that prevail only in local domains, then the proliferation is expected and not problematic. (shrink)

An account of analogical characterization is developed in which the following things are claimed.(1) Analogical predications are irreflexive, asymmetrical, atransitive and non-inversive. (2) Analogies A and B share role-similarity descriptions sufficiently abstract to overcome the differences between A and B. Analogies pivot on the point of limited similarity and substantial, even radical, difference. (3) The semantical theory for sentences making analogical attributions requires a distinction between (sentential) meaning as truth conditions and (sentential) meaning as a functional compound of the meanings (...) of contained lexical items. Analogical sentences possess both kinds of meaning. They are true via their truth conditions and would be false via their lexical meanings. The distinctive feature of the lexical meaning of analogical sentences is the tightness of constraints on closure. The implications of analogical sentences, given their lexical meanings, though there, aren't drawn. It is in this sense that analogies are made and not found. (shrink)

The longstanding species problem in biology has a history that suggests a solution, and that history is not the received history found in many texts written by biologists or philosophers. The notion of species as the division into subordinate groups of any generic predicate was the staple of logic from Aristotle through the middle ages until quite recently. However, the biological species concept during the same period was at first subtly and then overtly different. Unlike the logic sense, which relied (...) on definitions of the essence of both genus and species, biological species from the time of Epicurus were consistently considered to involve a reproductive element: in short, living species relied not on essential definitions, but on the generative cause, which might not be definable. I term this the generative conception of species: species were the generation by reproduction of form. This undercuts the claim that species before Darwin were essentialist, and divorces the notion of a type from that of essence. In fact, as late as the end of the nineteenth century, logicians explicitly treated biological “species” as a homonym only of logical essentialist species, and permitted considerable deviation from the type or form. At every point, species in logic were thought to be a subset, in effect, of some more general notion. I sketch a history of both philosophical and biological traditions of the species concept, before turning to the current conceptions. These are reconsidered in the light of this history, and in particular Mayr’s changing views are shown to be somewhat Whiggish, historiographically. Of the many touted biological species concepts, only one of which (Mayr’s) is called _the_ Biological Species Concept, none appears to capture all the relevant facts, intuitions, and operational requirements of biology. Cladistic conceptions, however, have much in common with the older philosophical literature, in that the natural group of cladism is the clade, or monophyletic group. After considering the Individuality Thesis, and the metaphysics of species, we see that species are the most particular terminal taxa in a clade, and that they are “defined” in terms of the particular synapomorphies, or evolved characters, that are causally responsible for keeping the lineages that organisms form distinct from one another. In this way, we can remain within the generative conception of species that has been in play for over two millennia, and yet avoid the pitfalls of prior attempts to find a universal conception of species. (shrink)

The phrase _secundum quid et simpliciter_ is the Latin expression translating and labelling the sophism described by Aristotle as connected with the use of some particular expression “absolutely or in a certain respect and not in its proper sense.” This paper presents an overview of the analysis of this fallacy in the history of dialectics, reconstructing the different explanations provided in the Aristotelian texts, the Latin and medieval dialectical tradition, and the modern logical approaches. The _secundum quid_ emerges as a (...) strategy that is based on the pragmatic dimension of arguments, and in particular the complex passage from an utterance (what is said) to its logical form (a proposition in an argument). The medieval and modern logical theories attempted to explain from different philosophical perspectives how the pragmatically enriched semantic representation can be achieved, justified, and most importantly manipulated. The different analyses of this fallacy bring to light various dimensions of the pragmatics of arguments, and the complex interdependence between context, meaning, and inferences. (shrink)

The fallacy of ignoring qualifications, or secundum quid et simpliciter, is a deceptive strategy that is pervasive in argumentative dialogues, discourses, and discussions. It consists in misrepresenting an utterance so that its meaning is broadened, narrowed, or simply modified to pursue different goals, such as drawing a specific conclusion, attacking the interlocutor, or generating humorous reactions. The “secundum quid” was described by Aristotle as an interpretative manipulative strategy, based on the contrast between the “proper” sense of a statement and its (...) meaning taken absolutely or in a certain respect. However, how can an “unqualified” statement have a proper meaning different from the qualified one, and vice versa? This “linguistic” fallacy brings to light a complex relationship between pragmatics, argumentation, and interpretation. The secundum quid is described in this paper as a manipulative argument, whose deceptive effect lies in its pragmatic dimension. This fallacy is analyzed as a strategy of decontextualization lying at the interface between pragmatics and argumentation and consisting of the unwarranted passage from an ut-terance to its semantic representation. By ignoring the available evidence and the presumptive interpretation of a statement, the speaker places it in a different context or suppresses textual and contextual evidence to infer a specific meaning different from the presumable one. (shrink)

In the middle of last century metaphysics was widely criticized, ridiculed, and committed to the flames. During this period a handful of philosophers, against several anti-metaphysical trends, defended metaphysics and articulated novel metaphysical doctrines. Donald C. Williams was one of these philosophers. But while his contributions to metaphysics are well known his defence of metaphysics is not and yet it played a key part in the development and revival of metaphysics. In this paper I present his defence of metaphysics in (...) its historical context. I also show how his defence is relevant in response to recent attacks on metaphysics. (shrink)

The studies that make up this book were written and brought together to honor the memory of Jan Pinborg. His unexpected death in 1982 at the age of forty-five shocked and saddened students of medieval philosophy everywhere and left them with a keen sense of disappoint ment. In his fifteen-year career Jan Pinborg had done so much for our field with his more than ninety books, editions, articles, and reviews and had done it all so well that we recognized him (...) as a leader and counted on many more years of his scholarship, his help, and his friendship. To be missed so sorely by his international colleagues in an academic field is a mark of Jan's achievement, but only of one aspect of it, for historians of philosophy are not the only scholars who have reacted in this way to Jan's death. In his decade and a half of intense productivity he also acquired the same sort of special status among historians of linguistics, whose volume of essays in his memory is being G. L. Bursill-Hall almost simultane published under the editorship of ously with this one. Sten Ebbesen, Jan's student, colleague, and successor as Director of the Institute of Medieval Greek and Latin Philology at the University of Copenhagen, has earned the gratitude of all of us by memorializing Jan 1 in various biographical sketches, one of which is accompanied by a 2 complete bibliography of his publications. (shrink)

This paper argues for a reinterpretation of Aristotle's concept of an enthymeme and also his wider informal logic in terms of arguments that are defeasible. They are represented by forms of argument that are called argumentation schemes, considered to be similar to forms of argument found in deductive logic, but different from the foregoing in virtue of their being defeasible. Indeed, the most interesting schemes have been put forward as a helpful way of characterizing structures of human reasoning that have (...) proved troublesome to model deductively. The paper sheds new light on Aristotle's topics and how to dene `enthymeme'. If the traditional denition of an enthymeme in logic accepted for over two thousand years is a misnomer, the question is raised whether we ought to redene it as a defeasible argumentations scheme or leave things as they are. (shrink)

Most recent discussions of John Stuart Mill’s System of Logic (1843) neglect the fifth book concerned with logical fallacies. Mill not only follows the revival of interest in the traditional Aristotelian doctrine of fallacies in Richard Whately and Augustus De Morgan, but he also develops new categories and an original analysis which enhance the study of fallacies within the context of what he calls ‘the philosophy of error’. After an exploration of this approach, the essay relates the philosophy of error (...) to the discussion of truth and error in chapter two of On Liberty (1859) concerned with freedom of thought and discussion. Drawing on Socratic and Baconian perspectives, Mill defends both the traditional study of logic against Jevons, Boole, De Morgan, and others, as well as the study of fallacies as the key to maintaining truth and its dissemination in numerous fields, such as science, morality, politics, and religion. In Mill’s view the study of fallacies also liberates ordinary people to explore the truth and falsity of ideas and, as such, to participate in society and politics and develop themselves as progressive beings. (shrink)

This essay presents a skeleton of a potential conceptual framework for human flourishing in a free society. Its aim is to present a diagram that illustrates the ways in which its topics relate to one another and why they do. It argues for a plan of conceptualization rather than for the topics themselves. It emphasizes the interconnections among the components of the schema presented. It sees an essential interconnection between objective concepts, arguing that all of the disciplines of human action (...) can be integrated into a paradigm of human flourishing based on the nature of man and the world. (shrink)

It is my intention in this thesis to demonstrate that there exists a clear and explicit formal relationship between the seemingly exclusive descriptions of spatio-temporal and purely temporal continuity, and further, that this relationship manifests itself within our most fundamental understanding of the physical world itself, namely; within our understanding of the identity, diversity and re-identification of material bodies. It may therefore be claimed that behind that cultural understanding which leads us to imagine that the physical world is located in (...) both space and time, whereas our thoughts and feelings are located in time alone, there lies a formal logical framework, or an explicit formal description of how being in space and time relates to being in time alone - leading us to wonder, perhaps, whether these two things are really as distinct as we might at first imagine. That I should then go on to apply to this analysis a philosophical interpretation of Bergson's conception of the relationship between the intuition and the intellect is of lesser importance - indicating as it does little more than my own philosophical inclinations. However, something will be gained, I hope, from this further exercise. Along the way it will allow me to clarify a number of technical points of which the general philosopher may be unaware; for example the unobservable nature of numerical identity and re-identification, the importance of the principle of special relativity to the topic of mind and the technical difficulties of claiming that mental events are 'in time' at all. Notwithstanding these latter points, however, the intentions of this work are predominantly analytical and are adequately described as an attempt to consolidate spatio-temporal and purely temporal description under a unified logical framework. (shrink)

The vision of natural kinds that is most common in the modern philosophy of biology, particularly with respect to the question whether species and other taxa are natural kinds, is based on a revision of the notion by Mill in A System of Logic. However, there was another conception that Whewell had previously captured well, which taxonomists have always employed, of kinds as being types that need not have necessary and sufficient characters and properties, or essences. These competing views employ (...) different approaches to scientific methodologies: Mill’s class-kinds are not formed by induction but by deduction, while Whewell’s type-kinds are inductive. More recently, phylogenetic kinds (clades, or monophyletic-kinds) are inductively projectible, and escape Mill’s strictures. Mill’s version represents a shift in the notions of kinds from the biological to the physical sciences. (shrink)

Inductive generalization asserts that what obtains in known instances can be generalized to all. Its original form is enumerative induction, the earliest form of inductive inference, and it has been elaborated in various ways, largely with the goal of extending its reach. Its principal problem is that it supplies no intrinsic notion of strength of support so that one cannot tell if the generalization has weak or strong support.

Three distinctly different interpretations of Aristotle’s notion of a sullogismos in Prior Analytics can be traced: (1) a valid or invalid premise-conclusion argument (2) a single, logically true conditional proposition and (3) a cogent argumentation or deduction. Remarkably the three interpretations hold similar notions about the logical relationships among the sullogismoi. This is most apparent in their conflating three processes that Aristotle especially distinguishes: completion (A4-6)reduction(A7) and analysis (A45). Interpretive problems result from not sufficiently recognizing Aristotle’s remarkable degree of metalogical (...) sophistication to distinguish logical syntax from semantics and, thus, also from not grasping him to refine the deduction system of his underlying logic. While it is obvious that Aristotle most often uses ‘sullogimos’ to denote a valid argument of a certain kind, we show that at Prior Analytics A4-6, 7, 45 Aristotle specifically treats a sullogismos as an elemental argument pattern having only valid instances and that such a pattern then serves as a rule of deduction in his syllogistic logic. By extracting Aristotle’s understanding of three proof-theoretic processes, this paper provides new insight into what Aristotle thinks reasoning syllogistically is and, moreover, it resolves three problems in the most recent interpretation that takes a sullogismos to be a deduction. (shrink)

John Cook Wilson (1849–1915) was Wykeham Professor of Logic at New College, Oxford and the founder of ‘Oxford Realism’, a philosophical movement that flourished at Oxford during the first decades of the 20th century. Although trained as a classicist and a mathematician, his most important contribution was to the theory of knowledge, where he argued that knowledge is factive and not definable in terms of belief, and he criticized ‘hybrid’ and ‘externalist’ accounts. He also argued for direct realism in perception, (...) criticizing both empiricism and idealism, and argued for a moderate nominalist view of universals as being in rebus and only ‘apprehended’ by their particulars. His influence helped swaying Oxford away from idealism and, through figures such as H. A. Prichard, Gilbert Ryle, or J. L. Austin, his ideas were also to some extent at the origin of ‘moral intuitionism’ and ‘ordinary language philosophy’ which defined much of Oxford philosophy until the second half of the twentieth-century. Nevertheless, his name and legacy were all but forgotten for generations after World War II. Still, his views on knowledge are with us today, being in part at work in the writings of philosophers as diverse as John McDowell, Charles Travis, and Timothy Williamson. (shrink)

Philosophy becomes speculative when it raises questions about the ultimate nature of being and thought. What does it mean to be? What does it mean to think? How are being and thought related? What does it mean to ask these questions? These questions have occupied a central place in philosophy throughout history, but have led a shadow existence in twentieth-century thought, which has cut the tie between reason and these fundamental questions, leaving the questions in the twilight, and reason instrumentalised. (...) A.N. Whitehead (1861-1947), one of the founders of analytic philosophy and co-author (with Bertrand Russell) of Principia Mathematica, is one of the few contemporary thinkers to have developed an explicit speculative philosophy. Unsurprisingly, his philosophy has played a marginal role in academic debates. In this study, the methodological foundation of Whitehead’s speculative thought is reconstructed. On the basis of a systematic and historical examination of the nature of the question of being, Whiteheads ontology of the event as the passage into novelty emerges in its full scope, allowing the reader to understand why and to what extent Whitehead has walked a different path than other contemporary thinkers. His philosophy contains a conception of reason that is not alien to newness and creativity while being more than procedural or pragmatic, and a mode of understanding existence that brings out the acuteness of freedom, value and legitimacy, as well as the unity of things, of thought and nature. In order to show what is really happening in this philosophy, the received interpretation of Whitehead’s ontology is radically dismantled. The central thought, that to be means to happen, is explained in a process of reiteration and gradual clarification, examining traditional philosophical problems in metaphysics and epistemology (on topics like: nature and matter, knowledge, categorical structure, freedom and necessity, truth and meaning, modality) from its perspective. What emerges is a philosophy in which the temporality of being, when taken seriously, changes the status of familiar problems and dualisms and offers possibilities for thought, which previously did not exist. Whitehead “hears” the classical questions of philosophy in a new way. Beyond the trenches of twentieth-century philosophy, Whitehead’s speculative thinking contains many elements that will be of value to those studying the foundations of thought today and looking for new directions. In a time when the dualism of nature and man is maintained cynically in our economies and dismantled, but only in a biologistic fashion and therefore only seemingly, as a cover-up, in science and philosophy, Whitehead’s new and creative way of hearing, and answering, old questions about ultimate concerns, when understood properly, is more up to date than ever before. (shrink)

Proposes a new way of understanding the nature of metaphysics, focusing on nonreductionist emergence theory, both in ancient and modern philosophy, as well as in contemporary philosophy of science.

Bayesian reasoning has been applied formally to statistical inference, machine learning and analysing scientific method. Here I apply it informally to more common forms of inference, namely natural language arguments. I analyse a variety of traditional fallacies, deductive, inductive and causal, and find more merit in them than is generally acknowledged. Bayesian principles provide a framework for understanding ordinary arguments which is well worth developing.

The question of whether or not to partition data for the purposes of inferring phylogenetic hypotheses remains controversial. Opinions have been especially divided since Kluge's (1989, Systematic Zoology 38, 7–25) claim that data partitioning violates the requirement of total evidence (RTE). Unfortunately, advocacy for or against the RTE has not been based on accurate portrayals of the requirement. The RTE is a basic maxim for non-deductive inference, stipulating that evidence must be considered if it has relevance to an inference. Evidence (...) is relevant if it has a positive or negative effect on a given conclusion. In the case of ℈partitioned’ phylogenetic inferences, the RTE is violated, and the basis for rational belief in any conclusion is compromised, unless it is shown that the partitions are evidentially irrelevant to one another. The goal of phylogenetic systematics is to hypothesize past causal conditions to account for observed shared similarities among two or more species. Such inferences are non-deductive, necessitating consideration of the RTE. Some phylogeneticists claim the parsimony criterion as justification for the RTE. There is no relation between the two – parsimony is a relation between a hypothesis and causal question(s). Parsimony does not dictate the content of premises prior to an inference. ℈Taxonomic congruence,’ ℈supertrees,’ and ℈conditional combination’ methods violate the RTE. Taxonomic congruence and supertree methods also fail to achieve the intended goal of phylogenetic inference, such that ℈consensus trees’ and ℈supertrees’ lack an empirical basis. ℈Conditional combination’ is problematic because hypotheses derived from partitioned data cannot be compared – a causal hypothesis inferred to account for a set of effects only has relevance to those effects, not any comparative relevance to other causal hypotheses. A similar problem arises in the comparisons of hypotheses derived from different causal theories. (shrink)

In the Posterior Analytics (I 6, 75a18–27) Aristotle discusses a puzzle which endangers the possibility of inferring a non-necessary conclusion. His solution relies on the distinction between the necessity of the conclusion's being the case and the necessity of admitting the conclusion once one has admitted the premisses. The former is a factual necessity, whereas the latter is meant to be a normative or deontic necessity that is independent of the facts stated by the premisses and the conclusion. This paper (...) maintains that Aristotle resorts to this distinction because he thinks that, as long as it is conceived as a factual relation, logical consequence cannot exist independently of the facts expressed by the premisses and the conclusion. As a corollary, the necessity of such a consequence relation always requires the necessity of these facts. Aristotle holds this factual conception of logical consequence responsible for the puzzle, since it cannot account for valid syllogisms with contingent or false premisses. The alternative conception of necessity is then introduced by him in order to make good this deficiency. The distinction between the necessity of being and the necessity of saying was revived by the Oxford logician E. W. B. Joseph, and taken over by Frank Ramsey in his seminal Truth and Probability, but has not received attention from recent interpreters of Aristotle's logic. This paper, however, argues that, in spite of its intrinsic interest, the distinction bore no significant fruit in Aristotle's logical doctrine. (shrink)

Populism is on the rise, especially in Western Europe. While it is often assumed that populist actors have a tendency for fallacious reasoning, this has not been systematically investigated. We analyze the use of informal fallacies by right-wing populist politicians and their representation in the media during election campaigns. We conduct a quantitative content analysis of press releases of right-wing populist parties and news articles in print media during the most recent elections in the United Kingdom and Switzerland in 2015. (...) The results show that fallacies are used in more than a third of all analyzed texts and overwhelmingly co-occur with populist key messages. Moreover, fallacies occur more often in populist parties’ press releases than in news articles and are more common in Switzerland compared to the United Kingdom. This study confirms the argument that populist actors use fallacies in combination with populist claims. (shrink)

In this paper it is shown how plausible reasoning of the kind illustrated in the ancient Greek example of the weak and strong man can be analyzed and evaluated using a procedure in which the pro evidence is weighed against the con evidence using formal, computational argumentation tools. It is shown by means of this famous example how plausible reasoning is based on an audience’s recognition of situations of a type they are familiar with as normal and comprehensible in their (...) shared common knowledge. The paper extends previous work on this example by using three new multiagent argumentation schemes closely related to the scheme for argument from negative consequences. (shrink)

Aristotle studies syllogistic argumentation in Sophistical Refutations and Prior Analytics. In the latter he focuses on the formal and syntactic character of arguments and treats the sullogismoi and non-sullogismoi as argument patterns with valid or invalid instances. In the former Aristotle focuses on semantics and rhetoric to study apparent sullogismoi as object language arguments. Interpreters usually take Sophistical Refutations as considerably less mature than Prior Analytics. Our interpretation holds that the two works are more of a piece than previously believed (...) and, indeed, that Aristotle's treatment of fallacious reasoning presupposes the results of the formal theory. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Philosophy and Rhetoric 34.2 (2001) 93-112 [Access article in PDF] Enthymemes, Common Knowledge, and Plausible Inference Douglas Walton The study of enthymemes has always been regarded as important in logic, critical thinking, and rhetoric, but too often it is the formal or mechanistic aspect of it that has been in the forefront. This investigation will show that there is a kind of plausibilistic script-based reasoning, of a kind that (...) has mainly been studied in artificial intelligence, that should have a much more important role to play in the study of enthymemes. But then curiously, as will also be shown, this plausibilistic type of reasoning was familiar in the ancient world, to the Sophists, as well as to leading philosophers such as Plato and Aristotle. By linking this ancient notion of plausibility to the modern notion used in computer science, this investigation reveals an important basis for the enthymeme that has a type of logical structure in its own right, but also has an informal aspect.An enthymeme, in current usage, is an argument that has one or more premises, or possibly a conclusion, not explicitly stated in the text, but that needs to have these propositions explicitly stated to extract the complete argument from the text. Sometimes enthymemes are described as arguments with "missing premises." That vocabulary is awkward, however, because the nonexplicit statement that needs to be added can be a conclusion, at least in a minority of cases. To make the exposition below smoother, the term nonexplicit assumption will be used to cover either the case of a nonexplicit premise or that of a nonexplicit conclusion. The problem with enthymemes is that if the nonexplicit assumptions in an argument are supposed to be propositions used by the arguer (as opposed to just the propositions needed to make the argument structurally correct, according to some standard), reasonable people can have differences of opinion on what the nonexplicit assumptions are supposed to be. The problem is that filling in the missing parts of enthymemes depends on interpreting the natural language [End Page 93] in which the argument was put forward to try to determine what the speaker meant to say.The solution to the problem comes through the recognition that enthymemes rest not only on formal (structural) criteria, but also on informal criteria. One of the most important of these informal criteria is something often called "common knowledge" (Govier 1992; Freeman 1995). But as shown below in a set of selected case studies of enthymemes, "common knowledge" is not really a kind of knowledge at all. It is really plausibility, or eikos, something well known in the ancient world and often misleadingly translated as "probability." Curiously, Aristotle's original doctrine of the enthymeme was based on this notion of plausibility. This historical fact has often been a source of puzzlement and confusion, and sometimes it has even been taken to indicate a defect or contradiction in Aristotle's treatment of the enthymeme. However, the goal of this investigation is not primarily historical. It is to work out one of the most important required steps toward a solution to the problem of enthymemes. But to do this, it is necessary to come back to the ancient notion of plausible inference. 1. The problem with enthymemes Once you have any formal theory of inference, like syllogistic, for example, you will be confronted by cases of arguments in everyday discourse that meet all the requirements for a structurally correct inference except that some part or parts, usually a premise or a conclusion, is missing. By "missing" is meant that the proposition in question has not been explicitly stated in the text of discourse, even though it may be clear enough that the speaker (writer) was relying on it, or including it, as part of the argument. The classic example is the following inference: All men are mortal; therefore, Socrates is mortal. To evaluate such an argument, surely some account of the "hidden" or "missing" assumption needs to be taken. The problem with enthymemes (Burke 1985; Gough and Tindale 1985; Hitchcock 1985) is that, if given carte... (shrink)