This paper defends a counterexample to Modus Tollens, and uses it to draw some conclusions about the logic and semantics of indicative conditionals and probability operators in natural language. Along the way we investigate some of the interactions of these expressions with 'knows', and we call into question the thesis that all knowledge ascriptions have truth-conditions.

Topological relations such as inside, outside, or intersection are ubiquitous to our spatial thinking. Here, we examined how people reason deductively with topological relations between points, lines, and circles in geometric diagrams. We hypothesized in particular that a counterexample search generally underlies this type of reasoning. We first verified that educated adults without specific math training were able to produce correct diagrammatic representations contained in the premisses of an inference. Our first experiment then revealed that subjects who correctly judged (...) an inference as invalid almost always produced a counterexample to support their answer. Noticeably, even if the counterexample always bore a certain level of similarity to the initial diagram, we observed that an object was more likely to be varied between the two drawings if it was present in the conclusion of the inference. Experiments 2 and 3 then directly probed counterexample search. While participants were asked to evaluate a conclusion on the basis of a given diagram and some premisses, we modulated the difficulty of reaching a counterexample from the diagram. Our results indicate that both decreasing the counterexample density and increasing the counterexample distance impaired reasoning performance. Taken together, our results suggest that a search procedure for counterexamples, which proceeds object‐wise, could underlie diagram‐based geometric reasoning. Transposing points, lines, and circles to our spatial environment, the present study may ultimately provide insights on how humans reason about topological relations between positions, paths, and regions. (shrink)

Manley and Wasserman (2008) join the chorus of opposition to the possibility of conditional analysis of dispositions. But that score cannot be settled without more careful attention to the implicit philosophical methodology. Some of the opposition to such an analysis badly overestimates the effect of counterexamples, as if the Gettier example were sufficient to refute the possibility of conjunctive analysis of knowledge. A general objection to a form of analysis must satisfy a number of constraints, and Manley and Wasserman join (...) the chorus too in failing to satisfy them. Most significant is the optional presupposition that the conditional used in analysis will exhibit some sort of centring. We show that even a careful effort to repair and reform Manley and Wasserman's objection to provide a satisfactory argument requires, ultimately, appeal to centring. Worse, the particular positive proposal they offer is vulnerable to a minor variant of their own counterexample. (shrink)

The theory of causal Bayes nets [15, 19] is, from an empirical point of view, currently one of the most promising approaches to causation on the market. There are, however, counterexamples to its core axiom, the causal Markov condition. Probably the most serious of these counterexamples are EPR/B experiments in quantum mechanics (cf. [13, 23]). However, these are also the only counterexamples yet known from the quantum realm. One might therefore wonder whether they are the only phenomena in the quantum (...) realm that create problems for causal Bayes nets. The aim of this paper is to demonstrate that not only the phenomenon of quantum correlations in EPR/B experiments create problems for causal Bayes nets, but also the temporal evolution of quantum systems, which is described as dualistic by quantum mechanics. For this purpose, it is shown that single photon experiments in a Mach-Zehnder interferometer (MZI) violate the causal Markov condition as well. It is then argued, however, that the Markov violation does not occur under the de Broglie-Bohm interpretation of Bohmian mechanics. (shrink)

David Makinson has argued that the compelling character of counterexamples to the Recovery Condition on contraction is due to an appeal to justificational structure. In “naked theories” where such structure is ignored or is not present, Recovery does apply. This note attempts to show that Makinson is mistaken on both counts. Recovery fails when no appeal is made to justificational structure.

In this essay, I present a straightforward counterexample to the Uniqueness Thesis, which holds, roughly speaking, that there is a unique rational response to any particular body of evidence.

We exhibit several counterexamples showing that the famous Serrin's symmetry result for semilinear elliptic overdetermined problems may not hold for partially overdetermined problems, that is when both Dirichlet and Neumann boundary conditions are prescribed only on part of the boundary. Our counterexamples enlighten subsequent positive symmetry results obtained by the first two authors for such partially overdetermined systems and justify their assumptions as well.

Harmony and conservative extension are two criteria proposed to discern between acceptable and unacceptable rules. Despite some interesting works in this field, the exact relation between them is still not clear. In this article, some standard counterexamples to the equivalence between them are summarized, and a recent formulation of the notion of stability is used to express a more refined conjecture about their relation. Then Prawitz's proposal of a counterexample based on the truth predicate to this refined conjecture is (...) shown to rest on dubious assumptions. As a consequence, two new counterexamples are proposed: one uses the extension of logic with a small amount of arithmetic, while the other uses the extension of a small fragment of arithmetic with a problematic operator defined by Peano. It is argued that both these new counterexamples work fine to reject the conjecture and that the last one works also as a rejection of harmony as a complete criterion of acceptability of rules. (shrink)

In his book God and Necessity and in four subsequent papers, Brian Leftow argues against metaphysical theories which hold that “God’s nature makes necessary truths true or gives rise to their truthmakers,” asserting that all such “deity theories commit us to the claim that God’s existence depends on there being truthmakers for particular necessary truths about creatures.” Leftow supports this by arguing that all deity theories entail that if it is untrue that water = H2O, then God does not exist. (...) This paper presents a counterexample deity theory along with a synopsis of its correlative theory of truth and truthmaking. (shrink)

Showing that the premises of an argument are not sufficient for (viz., do not entail) a conclusion a conclusion involves citing a counterexample that would show the premises of the argument to be true and the conclusion false. This paper distinguishes counterexamples by analogy (an argument with the same form as argument against which it is advanced but where it is clearly the case that the premises are true and the conclusion is false), counterexamples by possible conjunction (a conjunction (...) of the premises and the negation of the conclusion), and counter-arguments (arguments directed against the truth of the conclusion). After detailing the logical differences between these concepts, the paper describes the pedagogical significance of this distinction and provides an assortment of test exercises for students. (shrink)

Two alternative accounts have emerged as viable competitors to the forerunning counterfactual comparative account in the recent debate concerning the nature of harm. These are the “non-comparative statebased account of harm ” defended by Elizabeth Harman, the “event-based account of harm ” defended by Matthew Hanser. I raise one simple but serious counterexample involving “non-regrettable disabilities” that applies to both of these alternative accounts but that is avoided by the counterfactual comparative account. I point out that my counterexample (...) is one instance of a broader problem for alternatives to the counterfactual comparative account. The problem is that each of them divorces the concept of harm from the intuitive idea that we have moral and prudential reasons to avoid it. (shrink)

The paper deals with the epistemological problems posed by the application of the modus ponens rule in cognitive processing of distributed information. Distinguishing the deductive correctness of a rule of inference from its normativity for rational belief, we consider ‘counterexamples’ of modus ponens proposed in modern epistemology of logic that endanger not its model-theoretic validity, but epistemic rationality for boundedly rational cognitive agents. We explain the epistemic lacunas in the closure of knowledge according to modus ponens revealed by Dretske’s ‘counterexamples’ (...) by a variety of standards of validity that go beyond ‘common sense’. However, the epistemic ‘counterexamples’ of modus ponens proposed by McGee, Kolodny and MacFarlane require, in our opinion, an appeal to less obvious epistemic phenomena, which can be discovered by reasoning for interpretation. We demonstrate that the supposed ‘counterexamples’ to modus ponens do not conflict with either the epistemic neutrality of logic or its epistemic relevance to boundedly rational agents. On the contrary, the appeal to reasoning for interpretation, which is needed to resolve the difficulties caused by these ‘counterexamples’, helps to achieve a balance between the epistemic constraints of reasoning agents and the logical requirements for the correctness of their interpretive and deductive cognitive operations. (shrink)

We propose an original use of techniques from random graph theory to find a Monadic ∑ 1 1 sentence without an asymptotic probability. Our result implies that the 0-1 law fails for the logics ∑ 1 1 and ∑ 1 1 . Therefore we complete the classification of first-order prefix classes with or without equality, according to the existence of the 0-1 law for the corresponding ∑ 1 1 fragment. In addition, our counterexample can be viewed as a single (...) explanation of the failure of the 0-1 law of all the fragments of existential second-order logic for which the failure is already known. (shrink)

Corcoran, J. 2005. Counterexamples and proexamples. Bulletin of Symbolic Logic 11(2005) 460. -/- John Corcoran, Counterexamples and Proexamples. Philosophy, University at Buffalo, Buffalo, NY 14260-4150 E-mail: [email protected] Every perfect number that is not even is a counterexample for the universal proposition that every perfect number is even. Conversely, every counterexample for the proposition “every perfect number is even” is a perfect number that is not even. Every perfect number that is odd is a proexample for the existential proposition (...) that some perfect number is odd. Conversely, every proexample for the proposition “some perfect number is odd” is a perfect number that is odd. As trivial these remarks may seem, they can not be taken for granted, even in mathematical and logical texts designed to introduce their respective subjects. One well-reviewed book on counterexamples in analysis says that in order to demonstrate that a universal proposition is false it is necessary and sufficient to construct a counterexample. It is easy to see that it is not necessary to construct a counterexample to demonstrate that the proposition “every true proposition is known to be true” is false–necessity fails. Moreover the mere construction of an object that happens to be a counterexample does not by itself demonstrate that it is a counterexample–sufficiency fails. In order to demonstrate that a universal proposition is false it is neither necessary nor sufficient to construct a counterexample. Likewise, of course, in order to demonstrate that an existential proposition is true it is neither necessary nor sufficient to construct a proexample. This article defines the above relational concepts of counterexample and of proexample, it discusses their surprising history and philosophy, it gives many examples of uses of these and related concepts in the literature and it discusses some of the many errors that have been made as a result of overlooking the challenging subtlety of the proper use of these two basic and indispensable concepts. (shrink)

Kopec and Titelbaum collect five alleged counterexamples to Uniqueness, the thesis that it is impossible for agents who have the same total evidence to be ideally rational in having different doxastic attitudes toward the same proposition. I argue that four of the alleged counterexamples fail, and that Uniqueness should be slightly modified to accommodate the fifth example.

This paper considers five counterexamples to Mary Douglas's definition of dirt, one of which is extracted from a scene from George Eliot's novel Middlemarch and another from Marilyn Strathern's essay on anthropology at home.

I argue that there are at least two kinds of tacit premises; describe a certain type of counterexample against the validity of arguments, and then use it to identify one kind of tacit premise. I distinguish two classes of tacit premises on the grounds that they are discovered or constructed differently, they have different roles in an argument or causal explanation, and have different logical relations to each other.

The well‐known “Consequence Argument” for the incompatibility of freedom and determinism relies on a certain rule of inference; “Principle Beta”. Thomas Crisp and Ted Warfield have recently argued that all hitherto suggested counterexamples to Beta can be easily circumvented by proponents of the Consequence Argument. I present a new counterexample which, I argue, is free from the flaws Crisp and Warfield detect in earlier examples.

I discuss three recent counterexamples to the transitivity of grounding due to Jonathan Schaffer. I argue that the counterexamples don’t work and draw some conclusions about the relationship between grounding and explanation.

Frankfurt sets out to refute the principle according to which ‘a person is morally responsible for what he has done only if he could have done otherwise’ . Frankfurt devises a counterexample in which an agent is intuitively responsible even though she could not have done otherwise: Suppose someone – Black, let us say – wants Jones to perform a certain action. Black is prepared to go to considerable lengths to get his way, but he prefers to avoid showing (...) his hand unnecessarily. So he waits until Jones is about to make up his mind what to do, and he does nothing unless it is clear to him that Jones is going to decide to do something other than what he wants him to do. If it does become clear that Jones is going to decide to do something else, Black takes effective steps to ensure that Jones decides to do, and that he does do, what he wants him to do. Whatever Jones's initial preferences and inclinations, then, Black will have his way … Now suppose that Black never has to show his hand because Jones, for reasons of his own, decides to perform and does perform the very action Black wants him to perform. In that case, it seems clear, Jones will bear precisely …. (shrink)

Solves Vann McGee's counterexample to Modus Ponens within classical logic by disclosing the suppressed premises and bringing them /within/ the argument.

Ethicists and economists commonly assume that if A is all things considered better than B, and B is all things considered better than C, then A is all things considered better than C. Call this principle Transitivity. Although it has great conceptual, intuitive, and empirical appeal, I argue against it. Larry S. Temkin explains how three types of ethical principle, which cannot be dismissed a priori, threaten Transitivity: (a) principles implying that in some cases different factors are relevant to comparing (...) A to C than to comparing A to B or B to C; (b) principles of limited scope; (c) principles implying that morally relevant differences in degree can amount to differences in kind. My counterexamples employ a principle of type (c): pleasures and pains enormously different in intensity differ in kind. Temkin has also endorsed this type of counterexample, using arguments based on earlier drafts of this paper. (shrink)

The Direct Argument is an important argument for demonstrating that moral responsibility is incompatible with determinism because it makes no presuppositions about the nature of free will. One of the inference rules employed in the Direct Argument is rule A: If a proposition is broadly logically necessary, then it is true and no one is, nor ever has been, even partially morally responsible for the fact that the proposition is true. While inference rule A is assumed by all parties to (...) the debate, I demonstrate that the rule is invalid. (shrink)

A great deal of attention has been paid recently to the claim that traditional Frankfurt-type counterexamples to the Principle of Alternative Possibilities (PAP), which depend for their success on the presence of a perfectly reliable indicator (or prior sign ) of what an agent will freely do if left to act on his own, are guilty of begging the question against incompatibilists, since such indicators seem to presuppose a deterministic relation between an agent’s free action and its causal antecedents. Objections (...) of this sort have given rise to considerable efforts to construct alternative Frankfurt-type counterexamples that do not rely on prior signs of this kind and so do not presuppose determinism in a way that incompatibilists should find objectionable. One consequence of this shift in the way Frankfurt-type counterexamples are formulated is that it provides an opportunity for the forceful resurgence of certain versions of the so-called flicker defense of PAP. In this paper I develop two versions of the flicker defense, indicate their advantages over other versions of this strategy, and defend them against objections. Insofar as either of these is successful, it will show not only that PAP has yet to be falsified by any of the modified Frankfurt-type counterexamples currently on offer but that cases of this sort are in principle incapable of falsifying PAP. (shrink)

There is currently much discussion about how decision making should proceed when an agent's degrees of belief are imprecise; represented by a set of probability functions. I show that decision rules recently discussed by Sarah Moss, Susanna Rinard and Rohan Sud all suffer from the same defect: they all struggle to rationalize diachronic ambiguity aversion. Since ambiguity aversion is among the motivations for imprecise credence, this suggests that the search for an adequate imprecise decision rule is not yet over.

I survey Brouwer’s weak counterexamples to classical theorems, with a view to discovering what useful mathematical work is done by weak counterexamples; whether they are rigorous mathematical proofs or just plausibility arguments; the role of Brouwer’s notion of the creative subject in them, and whether the creative subject is really necessary for them; what axioms for the creative subject are needed; what relation there is between these arguments and Brouwer’s theory of choice sequences. I refute one of Brouwer’s claims with (...) a weak counterexample of my own. I also examine Brouwer’s 1927 proof of the negative continuity theorem, which appears to be a weak counterexample reliant on both the creative subject and the concept of choice sequence; I argue that it provides a good justification for the weak continuity principle, but it is not a weak counterexample and it does not depend essentially on the creative subject. (shrink)

Frankfurt sets out to refute the principle according to which ‘a person is morally responsible for what he has done only if he could have done otherwise’. Frankfurt devises a counterexample in which an agent is intuitively responsible even though she could not have done otherwise: Suppose someone – Black, let us say – wants Jones to perform a certain action. Black is prepared to go to considerable lengths to get his way, but he prefers to avoid showing his (...) hand unnecessarily. So he waits until Jones is about to make up his mind what to do, and he does nothing unless it is clear to him that Jones is going to decide to do something other than what he wants him to do. If it does become clear that Jones is going to decide to do something else, Black takes effective steps to ensure that Jones decides to do, and that he does do, what he wants him to do. Whatever Jones's initial preferences and inclinations, then, Black will have his way … Now suppose that Black never has to show his hand because Jones, for reasons of his own, decides to perform and does perform the very action Black wants him to perform. In that case, it seems clear, Jones will bear precisely …. (shrink)

According to a bedrock assumption in the current methodology of armchair philosophy, we may refute a theory aiming at analyzing a concept by providing a counterexample in which it intuitively seems that a hypothetical or real situation does not fit with what the theory implies. In this paper, we shall argue that this assumption is at most either untenable or otherwise useless in bringing about what is commonly expected from it.

We construct a normal extension of K4 with the finite model property whose minimal tense extension is not complete with respect to Kripke semantics.

A symposium on my *Objects: Nothing Out of the Ordinary* (2015). In response to Wallace, I attempt to clarify the dialectical and epistemic role that my arguments from counterexamples were meant to play, I provide a limited defense of the comparison to the Gettier examples, and I embrace the comparison to Moorean anti-skeptical arguments. In response to deRosset, I provide a clearer formulation of conservatism, explain how a conservative should think about the interaction between intuition and science, and discuss what (...) conservatives should say about scattered territories, clonal colonies, and arbitrary systems. In response to Tillman and Spencer, I fortify my original presentation of the debunking arguments by clarifying why, even while trees (if they exist) are paradigmatically causal, conservatives are meant to be rationally obstructed from believing that it is trees that are causing our tree beliefs. (shrink)

Commonsense holds that testimony transfers knowledge from a speaker to the hearer. If the speaker has knowledge, then the hearer acquires it. Call that sufficiency. And a hearer acquires knowledge only if the speaker has it to transfer. Call that necessity. This article reviews counterexamples--and some replies to those counterexamples--to both claims.

Choi (Philosophia, 38(3), 2010) argues that my counterexamples in Lee (Philosophia, 38(3), 2010) to the simple conditional analysis of disposition ascription are bogus counterexamples. In this paper, I argue that Choi’s arguments are not satisfactory and that my examples are genuine counterexamples.

It is often said that a correct logical system should have no counterexample to its logical rules and the system must be revised if its rules have a counterexample. If a logical system (or theory) has a counterexample to its logical rules, do we have to revise the system? In this paper, focussing on the role of counterexamples to logical rules, we deal with the question. -/- We investigate two mutually exclusive theories of arithmetic - intuitionistic and (...) paraconsistent theories. The paraconsistent theory provides a (strong) counterexample to Ex Contradiction Quodlibet (ECQ). On the other hand, the intuitionistic theory gives a (weak) counterexample to the Double Negation Elimination (DNE) of the paraconsistent theory. If any counterexample undermines the legitimate use of logical rules, both theories must be revised. -/- After we investigate a paraconsistent counterexample to ECQ and the intuitionist’s answer against it, we arrive at the unwelcome conclusion that ECQ has both a justification and a counterexample. Moreover, we argue that if a logical rule were abolished whenever it has a counterexample, a promising conclusion would be logical nihilism which is the view that there is no valid logical inference, and so a correct logical system does not exist. Provided that the logical revisionist is not a logical nihilist, we claim that not every counterexample is the ground for logical revision. While logical rules of a given system have a justification, the existence of a counterexample loses its role for logical revision unless the rules and the counterexample share the same structure. (shrink)

In recent years there has been a growing consensus that ordinary reasoning does not conform to the laws of classical logic, but is rather nonmonotonic in the sense that conclusions previously drawn may well be removed upon acquiring further information. Even so, rational belief formation has up to now been modelled as conforming to some fundamental principles that are classically valid. The counterexample described in this paper suggests that a number of the most cherished of these principles should not (...) be regarded as valid for commonsense reasoning. An explanation of this puzzling failure is given, arguing that a problem in the theory of rational choice transfers to the realm of belief formation. (shrink)

We provide counterexamples to some purported characterizations of dilation due to Pedersen and Wheeler :1305–1342, 2014, ISIPTA ’15: Proceedings of the 9th international symposium on imprecise probability: theories and applications, 2015).

Various formally valid counterexamples have been adduced against the Humean dictum that one cannot derive an “ought” from an “is.” There are formal rebuttals—some very sophisticated now (e.g., Charles R. Pigden’s and Gerhard Schurz’s)—to such counterexamples. But what follows is an intuitive and informal argument against them. I maintain that it is better than these sophisticated formal defenses of the Humean dictum and that it also helps us see why it implausible to think that we can be as decisive about (...) the truth or falsity of the dictum as both the formal counterexamples or formal barriers to them purport to be. (shrink)

Cantor's diagonal argument provides an indirect proof that there is no one-one function from the power set of a set A into A. This paper provides a somewhat more constructive proof of Cantor's theorem, showing how, given a function f from the power set of A into A, one can explicitly define a counterexample to the thesis that f is one-one.

I present two counterexamples to the recently back-in-favour truth-tracking account of knowledge: one involving a true belief resting on a counterfactually robust delusion, one involving a true belief acquired alongside a bunch of false beliefs. These counterexamples carry over to a recent modification of the theory due to Briggs and Nolan (2012), and seem invulnerable to a recent defence of the theory against known counterexamples, by Adams and Clarke (2005).

In this paper I will offer a comprehensive defense of the safety account of knowledge against counterexamples that have been recently put forward. In Sect. 2, I will discuss different versions of safety, arguing that a specific variant of method-relativized safety is the most plausible. I will then use this specific version of safety to respond to counterexamples in the recent literature. In Sect. 3, I will address alleged examples of safe beliefs that still constitute Gettier cases. In Sect. 4, (...) I will discuss alleged examples of unsafe knowledge. In Sect. 5, I will address alleged cases of safe belief that do not constitute knowledge for non-Gettier reasons. My overall goal is to show that there are no successful counterexamples to robust anti-luck epistemology and to highlight some major presuppositions of my reply. (shrink)

A standard view in legal and political theory is that, to a first approximation, (1) we should aim to bring about the most legitimate institutions possible to solve the problems that should be solved at the level of politics, and (2) individual people are required to follow the directives of legitimate institutions, at least insofar as those institutions have the authority to issue those directives, and insofar as other considerations are nearly equal.1 On this standard view, the philosophical analysis of (...) institutional legitimacy can appear to be of the utmost importance because it can seem to answer the most important questions about what we should actually do in the realm of law and politics, and because it may also seem to serve as the crucial bridge between ideal and nonideal theory, at least if institutional legitimacy is analyzed as it often is as a matter of doing well enough along dimensions that are familiar from ideal APA NEWSLETTER | PHILOSOPHY AND LAW theory (e.g., ideal justice, universal consent, respecting basic rights, social welfare maximization, and so on). In what follows I identify a number of possible counterexamples to this standard view, which suggest that there may be no straightforward connection between institutional legitimacy and facts about what reasons, rights, and duties we actually have, and what institutions we should actually try to bring about, contrary to what the standard view assumes. (shrink)