Moti Mizrahi (2013) presents some novel counterexamples to Hypothetical Syllogism (HS) for indicative conditionals. I show that they are not compelling as they neglect the complicated ways in which conditionals and modals interact. I then briefly outline why HS should nevertheless be rejected.

The debate over Hypothetical Syllogism is locked in stalemate. Although putative natural language counterexamples to Hypothetical Syllogism abound, many philosophers defend Hypothetical Syllogism, arguing that the alleged counterexamples involve an illicit shift in context. The proper lesson to draw from the putative counterexamples, they argue, is that natural language conditionals are context-sensitive conditionals which obey Hypothetical Syllogism. In order to make progress on the issue, I consider and improve upon Morreau’s proof of the invalidity of Hypothetical Syllogism. The improved proof (...) relies upon the semantic claim that conditionals with antecedents irrelevant to the obtaining of an already true consequent are themselves true. Moreover, this semantic insight allows us to provide compelling counterexamples to Hypothetical Syllogism that are resistant to the usual contextualist response. (shrink)

The discrepancy between English if's and the horseshoe is far from being negligible. That is not a reason for distrusting the horseshoe, which is useful so long as it is taken to mean just what it is defined to mean; and it is not a reason for distrusting our English if's, which in spite of their ambiguities are indispensable to our daily discourse. But it is a reason for distrusting the current logical pedagogy that leads students to take the two (...) as being intertranslatable. So if symbolic logic is to help us in our English arguments (and that should surely be one of its functions) it needs to be supplemented: it needs to be provided with additional symbols (presumably with the introduction of one or more primitive concepts) that will preserve the meaning of our various if's with greater accuracy. In the present paper I shall point in the direction of such a logic. I cannot undertake to develop it in a complete postulational form; but I can at least call attention to certain English locutions by which the required postulates should be guided. And I can venture to state some of the postulates using appropriate symbols. (shrink)

If we overlook no consequences when we assess the act, and no relevant features when we generalize, can it matter whether we ask 'What would happen if everyone did the same?' instead of 'What would happen if this act were performed?'? David Lyons has argued that it cannot. Two examples are here articulated to show that it can. The first turns on the way consequences are identified and assessed and in particular on the treatment accorded 'threshold consequences'. The second example (...) turns on the way in which the 'social context' of the act (what others would be doing) is taken into account in the generalization. Also included is a formal theory of conditionals from which implications are drawn for utilitarianism and with which I attempt to dispel certain doubts concerning cases employed in my arguments. (shrink)

I present some counterexamples to Adams's Thesis and explain how they undermine arguments that indicative conditionals cannot be truth-evaluable propositions.

The logician's central concern is with the validity of argument. A logical theory ought, therefore, to provide a general criterion of validity. This book sets out to find such a criterion, and to describe the philosophical basis and the formal theory of a logic in which the premises of a valid argument are relevant to its conclusion. The notion of relevance required for this theory is obtained by an analysis of the grounds for asserting a formula in a proof.

Peirce's example puts another nail in the coffin of the truth-functionality thesis. Conditionals are not truth-functional.

In this article, I present a schema for generating counterexamples to the argument form known as Hypothetical Syllogism with indicative conditionals. If my schema for generating counterexamples to HS works as I think it does, then HS is invalid for indicative conditionals.

Early commentators on David Lewis's account of counterfactuals noted that certain examples suggest that some counterfactuals with true antecedents and true consequents are false. Lewis's account has the consequence that all such counterfactuals are true, leaving us to choose between explaining away our intuitions about the examples in question or offering an alternative to Lewis's account. Here I argue that a simple modification of the familiar Lewisian truth conditions yields the intuitively correct verdicts about these examples, and so we can (...) take our intuitions about these examples at face value without any major departure from Lewis's approach to counterfactuals. (shrink)

I propose an amendment of Lewis's counterfactual analysis of causation, designed to overcome some difficulties concerning redundant causation.

This paper presents ConR (Conditional R), a logic of conditionals based on Anderson and Belnap''s system R. A Routley-Meyer-style semantics for ConR is given for the system (the completeness of ConR over this semantics is proved in E. Mares and A. Fuhrmann, A Relevant Theory of Conditionals (unpublished MS)). Moreover, it is argued that adopting a relevant theory of conditionals will improve certain theories that utilize conditionals, i.e. Lewis'' theory of causation, Lewis'' dyadic deontic logic, and Chellas'' dyadic deontic logic.

David Lewis (1941-2001) was Class of 1943 University Professor of Philosophy at Princeton University. His contributions spanned philosophical logic, philosophy of language, philosophy of mind, philosophy of science, metaphysics, and epistemology. In On the Plurality of Worlds, he defended his challenging metaphysical position, "modal realism." He was also the author of the books Convention, Counterfactuals, Parts of Classes, and several volumes of collected papers.

Counterfactuals is David Lewis' forceful presentation of and sustained argument for a particular view about propositions which express contrary to fact conditionals, including his famous defense of realism about possible worlds and his theory of laws of nature.

Counterfactuals are typically thought--given the force of Sobel sequences--to be variably strict conditionals. I go the other way. Sobel sequences and (what I call) Hegel sequences push us to a strict conditional analysis of counterfactuals: counterfactuals amount to some necessity modal scoped over a plain material conditional, just which modal being a function of context. To make this worth saying I need to say just how counterfactuals and context interact. No easy feat, but I have something to say on the (...) matter. (shrink)

This paper is obsolete. It is superseded by the book, Conditionals in Context, MIT Press, 2005.

"If you turn left at the next corner, you will see a blue house at the end of the street." That sentence -- a conditional -- might be true even though it is possible that you will not see a blue house at the end of the street when you turn left at the next corner. A moving van may block your view; the house may have been painted pink; a crow might swoop down and peck out your eyes. Still, (...) in some contexts, we might ignore these possibilities and correctly assert the conditional. In this book, Christopher Gauker argues that such context-relativity is the key to understanding the semantics of conditionals. Contexts are defined as objective features of the situation in which a conversation takes place, and the semantic properties of sentences -- conditionals included -- are defined in terms of assertibility in a context. One of the primary goals of a theory of conditionals has to be to distinguish correctly between valid and invalid arguments containing conditionals. According to Gauker, an argument is valid if the conclusion is assertible in every context in which the premises are assertible. This runs counter to what Gauker sees as a systematic misreading of the data by other authors, who judge arguments to be invalid if they can think of a context in which the premises are judged true and some other context in which the conclusion is judged false. Different schools of thought on conditionals reflect fundamentally different approaches to semantics. Gauker offers his theory as a motive and test case for a distinctive kind of semantics that dispenses with reference relations and possible worlds. (shrink)

Berit Brogaard and Joe Salerno (Counterfactuals and Context, ANALYSIS 68 (2008): 39-46) argue that the standard Stalnaker-Lewis counterexamples to hypothetical syllogism, strengthening the antecedent, and contraposition trade on a failure to hold fixed the context in which truth values are determined for the premises and conclusion in each counterexample. I argue that no contextual fallacy is committed in the standard counterexamples, and I offer a different view of what it is for a fact to be held fixed by a counterfactual (...) antecedent. On my view, for a fact to be held fixed is an epistemological matter, not a semantic matter. (shrink)

The logical properties of the 'if-then' connective of ordinary English differ markedly from the logical properties of the material conditional of classical, two-valued logic. This becomes apparent upon examination of arguments in conversational English which involve (noncounterfactual) usages of if-then'. A nonclassical system of propositional logic is presented, whose conditional connective has logical properties approximating those of 'if-then'. This proposed system reduces, in a sense, to the classical logic. Moreover, because it is equivalent to a certain nonstandard three-valued logic, its (...) decision procedure is almost as efficient as that of the classical logic. It therefore provides a rational and convenient system in which to formalize English arguments. (shrink)

This paper defends the view that standards, which are typically social in nature, play a role in determining whether a subject has knowledge. While the argument focuses on standards that pertain to reasoning, I also consider whether there are similar standards for memory and perception.Ultimately, I argue that the standards are context sensitive and, as such, we must view attributions of knowledge as indexical. I exploit similarities between this view and a version of the relevant alternatives reply to skepticism in (...) order to defend this reply against the objection that it is ad hoc. (shrink)

It is widely agreed that contraposition, strengthening the antecedent and hypothetical syllogism fail for subjunctive conditionals. The following putative counter-examples are frequently cited, respectively.

The paper has sought to show two things. One is that the apparent variety of Stalnaker and Lewis's counterexamples is misleading. Several of their examples are quite unsatisfactory because they depend on unguarded language behavior. There is in fact only one type of counterexample that is worth serious discussion, and that has the form of Barense's.For Barense's example, I try to show that it fails as a counterexample to transitivity because one of the premisses is false within the context of (...) the example. However, Barense's example is problematic for the Stalnaker-Lewis analysis, since their device for avoiding transitivity (rejecting the rule of conditional proof) does not in fact eliminate anomalous conclusions that can be drawn when both the premisses are taken as true.In sum, there appears to be no good reason to doubt thatif is transitive, that the antecedent of a conditional can be strengthened, and that the contrapositive can be inferred. And the rule of conditional proof does seem to capture a commonly accepted form of argument in support ofif-then statements. (shrink)

Reasoning with conditionals is often thought to be non-monotonic, but there is no incompatibility with classical logic, and no need to formalise inference itself as probabilistic. When the addition of a new premise leads to abandonment of a previously compelling conclusion reached by modus ponens, for example, this is generally because it is hard to think of a model in which the conditional and the new premise are true.

_Epistemic Logic_ studies statements containing verbs such as 'know' and 'wish'. It is one of the most exciting areas in medieval philosophy. Neglected almost entirely after the end of the Middle Ages, it has been rediscovered by philosophers of the present century. This is the first comprehensive study of the subject. Ivan Boh explores the rules for entailment between epistemic statements, the search for the conditions of knowing contingent propositions, the problems of substitutivity in intentional contexts, the relationship between epistemic (...) and modal logic, and the problems of composite and divided senses in authors ranging from Abelard to Frachantian. (shrink)

_Epistemic Logic_ studies statements containing verbs such as 'know' and 'wish'. It is one of the most exciting areas in medieval philosophy. Neglected almost entirely after the end of the Middle Ages, it has been rediscovered by philosophers of the present century. This is the first comprehensive study of the subject. Ivan Boh explores the rules for entailment between epistemic statements, the search for the conditions of knowing contingent propositions, the problems of substitutivity in intentional contexts, the relationship between epistemic (...) and modal logic, and the problems of composite and divided senses in authors ranging from Abelard to Frachantian. (shrink)

Epistemic logic is one of the most exciting areas in medieval philosophy. Neglected almost entirely after the end of the Middle Ages, it has been rediscovered by philosophers of the twentieth century. Epistemic Logic in the Later Middle Ages provides the first comprehensive study of the subject. Ivan Boh explores the contrast between epistemic and alethic conceptions of consequence, the general epistemic rules of consequence, the search for conditions of knowing contingent propositions, the problems of substitutivity in intentional contexts, the (...) considerations of epistemic/doxastic iterated modalities, and the problems of composite and divided senses in authors ranging from Abelard to Frachantian. Boh concludes with a comparison between medieval endeavors and the epistemic logic of our own times. Written in a clear and readable style with minimal symbolic apparatus, this book employs modern symbolism and conceptual frameworks, and complements the studies of the syntacticand semantic dimensions of medieval logic. (shrink)