Supposition is frequently invoked in many fields within philosophy, including aesthetics, philosophy of mind, philosophy of science and epistemology. However, there is a striking lack of consensus about the nature of supposition. What is supposition? Is supposition a sui generis type of mental state or is it reducible to some other type of mental state? These are the main questions Margherita Arcangeli explores in this book. She examines the characteristic features of supposition, along the dimensions (...) of phenomenology and emotionality, among others, in a journey through the imaginative realm. An informed answer to the question “What is supposition?” must involve an analysis of imagination, since supposition is so often defined in opposition to the latter. She assesses rival explanations of supposition putting forward a novel view, according to which the proper way of seeing supposition is as a primitive type of imaginative state. Supposition and the Imaginative Realm: A Philosophical Inquiry will be of great interest to students of philosophy of psychology, aesthetics, philosophy of mind, philosophy of science and epistemology. (shrink)

Williamson proposes that a "suppositional procedure" is a central heuristic we use to evaluate the truth of conditionals, though he also argues that this method often leads us astray. An alternative approach to the link between supposition and conditionals is to claim that we are guided by our antecedent conditional judgements in our supposing, and in particular in our determining which things follow from an initial supposition. This alternative explanation of the close link between conditionals and supposition (...) is developed and compared to Williamson's proposal. (shrink)

In 1981 I published an article called Early Supposition Theory. Then as now, the magisterial work on the subject was L.M. de Rijk’s Logica Modernorum and then as now any discussion of the topic would have to rely to a great extent on the texts published there. This means that many of the problems that existed then still remain, but a couple of important new studies and several new texts have been published in the meantime, so it may be (...) time to try to take stock of the situation. I will first look at the origin of the term suppositio and then at the chronology of our source texts. (shrink)

Rodden writes, “How do stories persuade us? How do they ‘move’—and move us? The short answer: by analogies.” Rodden’s claim is a natural first view, also held by others. This chapter considers the extent to which this view is true and helpful in understanding how fictional narratives, taken as wholes, may be argumentative, comparing it to the two principal (though not necessarily exclusive) alternatives that have been proposed: understanding fictional narratives as exhibiting the structure of suppositional argument, or the structure (...) of a kind of transcendental argument. Three key aspects of understanding a fictional narrative as an argument from analogy are identified. First, the argument will be relativistic or depend in an essential way upon the circumstances or intentions of the auditor or author. Second, in view of the first aspect, the argument will be loose and subjective, and accordingly less likely to yield knowledge. Third, the argument will not exhibit a distinctive structure applicable only to fictional narratives. I find that the third, and sometimes the first and second, of these same three aspects apply to understanding fictional narratives as suppositional arguments. I present considerations that point to a way of establishing that some extended fictions exhibit the structure of a kind of transcendental argument that is neither relativistic nor subjective, is knowledge-generating, and is uniquely applicable to fictional narratives. This supports literary cognitivism—the thesis that “literary fiction can be a source of knowledge in a way that depends crucially on its being fictional.”. (shrink)

Suppositional theories of conditionals take apparent similarities between supposition and conditionals as a starting point, appealing to features of the former to provide an account of the latter. This paper develops a novel form of suppositional theory, one which characterizes the relationship at the level of semantics rather than at the level of speech acts. In the course of doing so, it considers a range of novel data which shed additional light on how conditionals and supposition interact.

In a recent paper, Nils Kürbis argues that bilateral natural deduction systems in which assertions and denials figure as hypothetical assumptions are unintelligible. In this paper, I respond to this claim on two counts. First, I argue that, if we think of bilateralism as a tool for articulating discursive norms, then supposition of assertions and denials in the context of bilateral natural deduction systems is perfectly intelligible. Second, I show that, by transposing such systems into sequent notation, one can (...) make perfect sense of them without talking about supposition at all, just talking in terms of relations of committive consequence. I conclude by providing some motivation for adopting this normative interpretation of bilateralism on which this response to Kürbis’s argument is based. (shrink)

In ‘Reasoning and Regress’ I argued that inferring a conclusion from a set of propositions may simply consist in taking it that the conclusion follows from these propositions—thereby defusing familiar regress arguments. Sinan Dogramaci challenges the generality of this view, on the grounds that sometimes you may draw conclusions from no premisses that you believe. I respond by clarifying a distinction between the premisses of an argument from the reasons your conclusion is based upon. While suppositional reasoning may involve no (...) premisses in the former sense, it does not follow that it does not involve concluding something on the basis of reasons. This allows the view defended in ‘Reasoning and Regress’ to extend to suppositional reasoning. (shrink)

This paper follows up a suggestion by Paul Vincent Spade that there were two Medieval theories of the modes of personal supposition. I suggest that early work by Sherwood and others was a study of quantifiers: their semantics and the effects of context on inferences that can be made from quantified terms. Later, in the hands of Burley and others, it changed into a study of something else, a study of what I call global quantificational effect. For example, although (...) the quantifier in ‘¬∀xPx’ is universal, it can be seen globally as having an existential effect; this is because the formula containing it is equivalent to ‘∃x¬Px’. The notion of global effect can be explained in terms of the modern theory of normal forms. I suggest that early authors were studying quantifiers, and the terminology of the theory of personal supposition is a classification of kinds of quantifiers. In this theory, to say that a term has distributive supposition is to say, roughly, that it is quantified by a universal quantifying sign. Later authors turned this into a theory of global quantificational effect. In the later theory, to say that a term has distributive supposition is to say that the overall effect is as if the term were universally quantified with a quantifier taking (relatively) wide scope. The difference between these two approaches is illustrated by the fact that the term ‘man’ is classified as having distributive ("universal") supposition in ‘Not every man is running’ in the earlier theory, whereas in the later theory that term does not have distributive supposition; it has determinate ("existential") supposition. In the paper I explain these options, and I argue from several texts that the earlier and later medieval theories actually worked like this. In an appendix I make further efforts to clarify the obscure early accounts, as well as the nineteenth century "doctrine of distribution". The last section of the paper discusses the "purpose(s)" of supposition theory. (shrink)

A popular view maintains that supposition is a kind of cognitive mental state, very similar to belief in essential respects. Call this view “cognitivism about supposition”. There are at least three grades of cognitivism, construing supposition as (i) a belief, (ii) belief-like imagination or (iii) a species of belief-like imagination. I shall argue against all three grades of cognitivism and claim that supposition is a sui generis form of imagination essentially dissimilar to belief. Since for good (...) reasons (i) is not supported in the literature, I shall dwell on (ii) and (iii). Without further explanation supposition has been very often merely postulated as being nothing but belief-like imagination—that is, (ii). I shall show that at least two considerations undermine (ii). First, supposition and belief-like imagination are governed by different norms, more precisely the former is freer than the latter and requires minimal or no mental effort. Second, contrary to belief-like imagination, supposition is “cold”, in that it is typically dissociated from emotional reactions. Proponents of (iii) face the pressure of explaining these differences between supposition and belief-like imagination too. I shall argue that they have not sufficiently motivated the claim that supposition is belief-like. In particular they fail to accommodate precisely the dimensions of supposition pertaining to its normativity and emotionality. I shall close with a sketch of a new account of supposition. (shrink)

Informal logicians recognise the frequent use of unstated assumptions; some (e.g. Fisher) also recognise entertained arguments and recommend a suppositional approach (such as Mackie's) to conditional statements. It is here argued that these two be put together to make argument diagrams more accurate and subtle. Philosophical benefits also accrue: insights into Jackson's apparent violations of modus tollens and contraposition and McGee's counterexamples to the validity of modus ponens.

I undertake to examine the practice of Richard, Master of Abstractions, with respect to supposition in his dealing with the fallacy of figure of speech. His practice turns out to support the ‘single theory’ account of the theory of personal supposition, as does his treatment of a functional equivalent of simple supposition, but his practice of proposing additional solutions points to changing attitudes with respect to species as separate entities. Questions having to do with material supposition (...) and the like are completely absent, even in discussions where we might expect to find them. (shrink)

Suppositions can be introduced in either the indicative or subjunctive mood. The introduction of either type of supposition initiates judgments that may be either qualitative, binary judgments about whether a given proposition is acceptable or quantitative, numerical ones about how acceptable it is. As such, accounts of qualitative/quantitative judgment under indicative/subjunctive supposition have been developed in the literature. We explore these four different types of theories by systematically explicating the relationships canonical representatives of each. Our representative qualitative accounts (...) of indicative and subjunctive supposition are based on the belief change operations provided by AGM revision and KM update respectively; our representative quantitative ones are offered by conditionalization and imaging. This choice is motivated by the familiar approach of understanding supposition as `provisional belief revision' wherein one temporarily treats the supposition as true and forms judgments by making appropriate changes to their other opinions. To compare the numerical judgments recommended by the quantitative theories with the binary ones recommended by the qualitative accounts, we rely on a suitably adapted version of the Lockean thesis. Ultimately, we establish a number of new results that we interpret as vindicating the often-repeated claim that conditionalization is a probabilistic version of revision, while imaging is a probabilistic version of update. (shrink)

To suppose X means to pretend to change one's belief for the sake of the argument to include X. How to do so is a decision problem: of the many ways to modify one's beliefs to include X, one should choose the one that best fits with one's epistemic goals. I examine the role of suppositional reasoning in the evaluation of purported scientific explanations of various sorts, based on Hempel and Oppenheim's deductive-nomological and inductive-statistical explanations. First, I present for each (...) type of explanation the suppositional reasoning conditions it must satisfy. For example, the dipping of blue litmus paper in acid explains why it turned red only if, when one supposes that the litmus paper was not dipped in acid, one must also give up the belief that it turned red. Second, I argue that a specific decision making method should be used to determine how one is to change one's beliefs for the sake of the argument in each case. Third, I evaluate in detail whether purported explanations, both intuitively explanatory and intuitively non-explanatory satisfy these conditions. Fourth, I show that the suppositional reasoning conditions for explanations, when evaluated correctly, systematically solve the many counterexamples to the original Hempel-Oppenheim model. (shrink)

I. SUPPOSITION AND SIGNIFICATIONIn an insightful article on the medieval theory of supposition, Elizabeth Karger noted a remarkable development in the characterization of the material mode of supposition between William of Ockham and his contemporaries in the early fourteenth century and Paul of Venice and others at the turn of the fifteenth century.1. E. Karger, “La Supposition Materielle comme Supposition Significative: Paul de Venise, Paul de Pergula,” in A. Maierú, ed., English Logic in Italy in (...) the 14th and 15th Centuries (Naples, 1982), pp. 331–41. For William, material supposition is explicitly ‘non-significative’, while for Paul, every mode of supposition is a kind of signification.2. Paul of Venice, Logica Magna (Tractatus de Suppositionibus), ed. and trans. A. Perreiah (St. Bonaventure, 1971), p. 4: “nam omnis suppositio est significatio.” In particular, we can set these definitions in opposition. (shrink)

Suppositional reasoning can seem spooky. Suppositional reasoners allegedly (e.g.) “extract knowledge from the sheer workings of their own minds” (Rosa), even where the knowledge is synthetic a posteriori. Can literary fiction pull such a rabbit out of its hat? Where P is a work’s fictional ‘premise’, some hold that some works reason declaratively (supposing P, Q), imperatively (supposing P, do Q), or interrogatively (supposing P, Q?), and that this can be a source of knowledge if the reasoning is good. True, (...) I will argue, although only within the context of judicious critical interpretation. Further evident constraints include that the form of the suppositional reasoning needs to be declarative or imperative, and that the fictional ‘premise’ of the work needs to be a metaphysical counterfactual possibility, not merely a temporal counterfactual and not merely an epistemic possibility or probabilistic supposition. (shrink)

The material conditional and the suppositional analysis of the indicative conditional are based on different philosophical foundations and they leave important successes of their competitor unexplained. This paper unifies both accounts within a truth-functional, trivalent model of the suppositional analysis. In this model, we observe that the material and the suppositional conditional exhibit the same logical behavior while they have different truth conditions and different probabilities. The result is a unified semantic analysis that closes an important gap in the suppositional (...) story and explains the persistent appeal of the material conditional analysis for philosophers and psychologists of reasoning. (shrink)

In bilateral logic formulas are signed by + and –, indicating the speech acts assertion and denial. I argue that making an assumption is also speech act. Speech acts cannot be embedded within other speech acts. Hence we cannot make sense of the notion of making an assumption in bilateral logic. Attempts to solve this problem are considered and rejected.

Many fourteenth-century logicians took affirmative propositions to maintain that the subject term and the predicate term stand or supposit for the same. This is called the identity theory of predication by historians and praedicatio identica by Paul of Venice and others. The identity theory of predication was an important part of early fourteenth-century Trinitarian discussions as well, but what was called praedicatio identica by Duns Scotus and his followers in this context was something different. After some remarks on Scotus’s view (...) and its background, I shall analyse Adam Wodeham’s explanation of Scotus’s praedicatio identica and how he understood the assumptions pertaining to supposition in the Scotist approach. I also describe Wodeham’s own solution to Trinitarian sophisms, which did not deviate from the identity theory of predication. (shrink)

No início do século XIV, Raimundo Lúlio, contrapondo-se aos mestres em Artes por ele identificados como averroistae, desenvolveria não menos que dois métodos resolutivos de inconsistência, a fim de refutar aquelas teses filosóficas que divergem da fé cristã. Um deles serve-se de silogismos contraditórios capazes de expressar a estrutura de um argumento ad hominem, ao passo que o outro nada mais é do que uma reductio ad impossibile elaborada com base em suposições contraditórias. In the early fourteenth century, Ramond Lully, (...) opposed to university philosophers whom he identified as averroistae, developed no less than two methods for the resolution of inconsistency, in order to refute philosophical theses which diverge from the Christian faith. The first of these uses contradictory syllogisms expressing the structure of an ad hominem argument, while the other is a reductio ad impossibile produced with contradictory suppositions. (shrink)

In this paper, Ockham's theory of an ideal language of thought is used to illuminate problems of interpretation of his theory of truth. The twentieth century idea of logical form is used for finding out what kinds of atomic sentences there are in OckhamÕs mental language. It turns out that not only the theory of modes of supposition, but also the theory of supposition in general is insufficient as a full theory of truth. Rather, the theory of (...) class='Hi'>supposition is a theory of reference, which can help in the determination of truth values within the scope of simple predications. Outside this area, there are interesting types of sentences, whose truth does not depend on whether the terms supposit for the same things or not for the same things. (shrink)

We report the results of three experiments designed to assess the role of suppositions in human reasoning. Theories of reasoning based on formal rules propose that the ability to make suppositions is central to deductive reasoning. Our first experiment compared two types of problem that could be solved by a suppositional strategy. Our results showed no difference in difficulty between problems requiring affirmative or negative suppositions and very low logical solution rates throughout. Further analysis of the error data showed a (...) pattern of responses, which suggested that participants reason from a superficial representation of the premises in these arguments and this drives their choice of conclusion. Our second experiment employed a different set of suppositional problems but with extremely similar proofs in terms of the rules applied and number of inferential steps required. As predicted by our interpretation of reasoning strategies employed in Experiment 1, logical performance was very much higher on these problems. Our third experiment showed that problems that could be solved by constructing an initial representation of the premises were easier than problems in which this representation was not sufficient. This effect was independent of the suppositional structure of the problems. We discuss the implications of this research for theories of reasoning based on mental models and inference rules. (shrink)

The atheist who begins to argue his case by saying, ‘Suppose there is an omniscient Being of the sort in which Christians believe ...’ is employing a very familiar move in argumentation. However, most books on argumentation theory ignore ‘suppositions’ completely. Searle omits suppositions entirely from his taxonomy of speech acts and this appears to lead to a similar omission in Speech Acts in Argumentative Discussions by van Eemeren and Grootendorst.This paper argues that ‘suppositional argument’ is elegant, powerful and extremely (...) common, that the correct way to understand it is based on Gottlob Frege's distinction between ‘asserted’ and ‘unasserted’ propositions and hence that suppositions are neither assertions nor (and this is more important) assertives. The paper discusses the connections between suppositions and conditionals; it argues that argumentation theory which ignores suppositions is systematically misleading; and it concludes by indicating some possible developments in argumentation theory. (shrink)

In a 2002 article Stewart Cohen advances the “bootstrapping problem” for what he calls “basic justification theories,” and in a 2010 followup he offers a solution to the problem, exploiting the idea that suppositional reasoning may be used with defeasible as well as with deductive inference rules. To curtail the form of bootstrapping permitted by basic justification theories, Cohen insists that subjects must know their perceptual faculties are reliable before perception can give them knowledge. But how is such knowledge of (...) reliability to be acquired if not through perception itself? Cohen proposes that such knowledge may be acquired a priori through suppositional reasoning. I argue that his strategy runs afoul of a plausible view about how epistemic principles function; in brief, I argue that one must actually satisfy the antecedent of an epistemic principle, not merely suppose that one does, to acquire any justification by its means – even justification for a merely conditional proposition. (shrink)

In a recent paper, Sprenger (2019) advances what he calls a “suppositional” answer to the question of why a Bayesian agent’s degrees of belief should align with the probabilities found in statistical models. We show that Sprenger’s account trades on an ambiguity between hypothetical and subjunctive suppositions and cannot succeed once we distinguish between the two.

For the past three decades the theory of supposition (suppositio) has been a crux of scholarship in Medieval logic. Although supposition was one of the banner doctrines of the logic modernorum, its nature and purpose have remained elusive to modern interpreters. In this paper I outline an alternative approach to supposition theory. (edited).

In this article, we discuss the notion of merely confused supposition as it arose in the medieval theory of suppositio personalis. The context of our analysis is our formalization of William of Ockham's theory of supposition sketched in Mind 86 (1977), 109-13. The present paper is, however, self-contained, although we assume a basic acquaintance with supposition theory. The detailed aims of the paper are: to look at the tasks that supposition theory took on itself and to (...) use our formalization to relate them to more modern ideas; to explain the notion of merely confused supposition and to defend it against certain criticisms; and to discuss two issues closely related to the idea of merely confused supposition which we could not broach in a shorter article: the mode of supposition of terms in intensional contexts, and the possible existence of a fourth mode, often called suppositio copulatim. (shrink)

The article investigates how the problem of reference is treated in the theology of two pupils of Gilbert of Poitiers by means of suppo* terms. Supposition is for Gilbert an action performed by a speaker, not a property of terms, and he considers language as a system for communication between human beings: key notions are the ‘sense in the author’s mind’ and the ‘interpreter’s understanding’. In contrast, the two Porretans tend to objectify language as a formal system of terms. (...) Suppositio becomes in the Summa Zwettlensis the name itself as subject term in a proposition, and is divided into many kinds; formal rules are described which govern the influence of the predicate on the subject term’s denotation. In Everard of Ypres’ Dialogus Ratii et Everardi, supponere is a function of the name, and ‘human is a species of individuals’ is, as in some logical treatises and differently from Gilbert, a case of rhetorical transfer. (shrink)

Deductive reasoning shares with other forms of thinking a reliance on strategies, as shown by the results of three experiments on the nature and development of control strategies to solve suppositional deductions. These puzzles are based on assertors who may or may not be telling the truth, and their assertions about their status as truthtellers and liars. The first experiment shows that reasoners make backward inferences as well as forward inferences, to short-cut their way through the alternatives, and the generation (...) of suppositions is a source of difficulty. The second experiment establishes that the elimination of the suppositional status of an individual does not render problems easier. The third experiment shows that reasoners can improve their reasoning accuracy and speed spontaneously, without feedback, and it clarifies the transfer of strategies and their development. We discuss the implications of these data for alternative theories of suppositional deduction and for the relationship between reasoning and other forms of thinking such as problem solving. (shrink)

Case-based reasoning is a familiar method of evaluating sentences. But when applied to conditionals, it seems to lead to implausible conclusions. In this paper I argue that the problem arises from equating the probability of a conditional sentence on the evidential supposition of some condition with the conditional probability of the former, given the latter.

I propose to examine the issue of whether the ancient tradition in logic continued to be developed in the later medieval period from the vantage point of the relations between two specific groups of theories, namely the medieval theories of supposition and the (originally) ancient theories of fallacies. More specifically, I examine whether supposition theories absorbed and replaced theories of fallacies, or whether the latter continued to exist, with respect to one particular author, William of Ockham. I compare (...) different parts of Ockham's Summa Logicae, namely III-4 (on fallacies), and the final chapters of part I and first chapters of part II (on supposition). I conclude that there is overlap of conceptual apparatus and of goals (concerning propositions that must be distinguished) in Ockham's theories of supposition and of fallacies, but that the respective conceptual apparatuses also present substantial dissimilarities. Hence, theories of supposition are better seen as an addition to the general logical framework that medieval authors had inherited from ancient times, rather than the replacement of an ancient tradition by a medieval one. Indeed, supposition theories and fallacy theories had different tasks to fulfil, and in this sense both had their place in fourteenth century logic. (shrink)

Arguments and conditionals are powerful means language provides us to reason about possibilities and to reach conclusions from premises. These two kinds of constructions exhibit several affinities—e.g., they both come in different varieties depending on the mood; they share some of the same connectives (i.e., ‘then’); they allow for similar patterns of modal subordination. In the light of these affinities, it is not surprising that prominent theories of conditionals—old and new suppositionalisms as well as dynamic theories of conditionals—as well as (...) certain reductive theories of arguments tend to semantically assimilate conditionals and arguments. In this paper, I shall marshall some linguistic evidence as well as some theoretical considerations for thinking that, despite these similarities, arguments and conditionals should be given a different semantics and I shall lay out a framework that can capture at least some of their affinities while accounting for their outstanding differences. (shrink)

It has been widely accepted in the past and it remains accepted in many quarters even now, that an ontologically economical position is to be rejected if the corresponding Platonic or otherwise ontologically prodigal discourse cannot be translated, paraphrased or otherwise ‘reduced’ to discourse exhibiting a more economical ontology. Such an attitude is often accompanied by the claim that the prodigal ontology explains some important truthsandthe demand that the nominalist or fictionalist or economicalist provide an alternative explanation for those truths (...) — perhaps in terms of ontologically economical ersatz substitutes for the prodigal entities. (shrink)

Abstract I analyse the relationship between the Ramsey Test (RT) for the acceptance of indicative conditionals and the so-called problem of decision-instability. In particular, I argue that the situations which allegedly bring about this problem are troublesome just in case the relevant conditionals are evaluated by non-suppositional versions, e.g. causal/evidential, of the test. In contrast, a suppositional RT, by highlighting the metacognitive nature of the evaluation of indicative conditionals, allows an agent to run a simulation of such evaluation, without yet (...) committing her to the acceptance of such conditionals. I conclude that a suppositional interpretation of RT is superior to its nonsuppositional counterparts and by briefly showing that a suppositional RT is compatible with a deliberational decision theory. (shrink)

In the summer of 1980, I was privileged to be on the teaching staff of the Summer Institute on Medieval Philosophy held at Cornell University under the direction of Norman Kretzmann and the auspices of the Council for Philosophical Studies and the National Endowment for the Humanities. While I was giving a series of lectures on supposition theory, I went to my office one morning, and there under the door some anonymous wag from the Institute had slid the pen (...) and ink drawing you see in the graphic. It represents "Supposition" as a dragon, making a rude face at the viewer. The tail of the dragon is divided — not entirely accurately, as it turns out — into the various branches and subbranches of supposition. If the details are not altogether correct, the spirit is certainly understandable. I have absolutely no idea who the inspired artist was, but I have the original framed on the wall in my office. (shrink)

In a recent paper Paul Vincent Spade suggests that, although the medieval doctrine of the modes of personal supposition originally had something to do with the rest of the theory of supposition, it became, by the 14th century, an unrelated theory with no question to answer. By contrast, I argue that the theory of the modes of personal supposition was meant to provide a way of making understandable the idea that a general term in a categorical proposition (...) can be used to refer to the individual things that fall under it. Once that idea had been made acceptable, truth conditons for the various forms of categorical proposition could be given without any specific appeal to the ideas of descent and ascent in terms of which the modes had been defined. (shrink)

According to many forms of Externalism now popular in the Philosophy of Mind, the contents of our thoughts depend in part upon our physical or social milieu.1 These forms of Externalism leave unchallenged the thesis that the ~non-factive! attitudes we bear towards these contents are independent of physical or social milieu. This paper challenges that thesis. It is argued here that publicly forwarding a content as a supposition for the sake of argument is, under conditions not themselves guaranteeing the (...) existence of that state, sufficient for occupancy of the intentional state of supposing that content. Because a saying may literally create an intentional state, whether one is in such a state does not depend solely upon how things are within one’s skin. Rather, even leaving content fixed, the attitude borne toward that content depends in part upon what norms are in force in one’s milieu. (shrink)

'If' is one of the most important words in the English language, being used to express hypothetical thought. The use of conditional terms such as 'if' distinguishes human intelligence from that of all other animals. In this volume, Jonathan Evans and David Over present a new theoretical approach to understanding conditionals. The book draws on studies from the psychology of judgement and decision making, as well as philosophical logic.

Timothy Williamson contends that our primary cognitive heuristic for prospectively assessing conditionals, i.e., the suppositional procedure, is provably inconsistent. Our diagnosis is that stipulations about the nature of suppositional rejection are the likely source of these results. We show that on at least one alternative, and quite natural, understanding of the suppositional attitudes, the inconsistency results are blocked. The upshot is an increase in the reliability of our suppositional heuristics across a wider range of contexts. One interesting consequence of the (...) increased reliability is a proportional decrease in the plausibility of an error-theory that Williamson employs against widespread intuitions about the truth values of counterpossible conditionals. (shrink)

Although he does not have an explicit theory of supposition as is found in the works of Latin medieval philosophers, Avicenna has two doctrines giving something equivalent: the threefold distinction of quiddity, corresponding to a division of simple, personal and material supposition, and his analyses of truth conditions for categorical propositions, where sentential context determines in part the reference of their terms. While he does address which individuals are being referred to by the universal terms used there, Avicenna (...) concentrates more on the varied temporal durations of the predications being made. In Western terms, he has incorporated ampliation and restriction into the theory of supposition itself. (shrink)

Paul Spade argues that there is a tension between Ockham’s descriptions of the various types of supposition at Summa Logicae I.64 and a rule he provides at sl I.65. In later papers, Spade proposes a solution: a term supposits significatively just in case it supposits for everything it signifies. I evaluate Spade’s proposal and explore some of its implications. I show that it successfully resolves the tension and that it suggests a way to more precisely describe material and simple (...) supposition. I argue furthermore that Ockham is committed to the proposal by showing that uncontroversial features of his theory imply it. In doing so, I raise and refute three potential objections. Finally, I highlight and discuss a controversial result: self-signifying conventional terms can supposit materially. I argue that this result makes for a more satisfying theory. (shrink)