We investigate under what conditions contrary-to-duty (CTD) structures lacking temporal and action elements can be given a coherent reading. We argue, contrary to some recent proposals, that CTD is not an instance of defeasible reasoning, and that methods of nonmonotonic logics are inadequate since they are unable to distinguish between defeasibility and violation of primary obligations. We propose a semantic framework based on the idea that primary and CTD obligations are obligations of different kinds: a CTD obligation pertains to, or (...) pre-supposes, a certain context in which a primary obligation is already violated. This framework is presented initially as an extension of Standard Deontic Logic (SDL), a normal modal logic of type KD, and is illustrated by application to a series of examples. The concluding section is concerned with some resemblances between CTD and defeasible reasoning. We show first that the SDL-based framework contains a flaw and must be adjusted. A discussion of possible adjustments, including an alternative treatment in terms of a preference-based semantics, reveals difficulties that are reminiscent of problems in defeasible reasoning and intensional accounts of defeasible conditionals. (shrink)

‘If in this book harsh words are spoken about some of the greatest among the intellectual leaders of mankind, my motive is not, I hope, to belittle them. It springs rather from my conviction that, if our civilization is to survive, we must break with the habit of deference to great men.’ - Karl Popper, from the Preface Written in political exile during the Second World War and first published in two volumes in 1945, Karl Popper’s The Open Society and (...) Its Enemies is one of the most influential books of all time. Hailed by Bertrand Russell as a ‘vigorous and profound defence of democracy’, its now legendary attack on the philosophies of Plato, Hegel and Marx exposed the dangers inherent in centrally planned political systems and through underground editions become an inspiration to lovers of freedom living under communism in Eastern Europe. Popper’s highly accessible style, his erudite and lucid explanations of the thoughts of great philosophers and the recent resurgence of totalitarian regimes around the world are just three of the reasons for the enduring popularity of The Open Society and Its Enemies and why it demands to be read today and in years to come. (shrink)

Princeton University Press, 1974. This book is out of print, but can be downloaded as a pdf file (5 MB).

There was a long tradition in philosophy according to which good reasoning had to be deductively valid. However, that tradition began to be questioned in the 1960’s, and is now thoroughly discredited. What caused its downfall was the recognition that many familiar kinds of reasoning are not deductively valid, but clearly confer justification on their conclusions. Here are some simple examples.

"Dernières pensées" de Henri Poincaré. Mathématicien, physicien et philosophe français (1854-1912).

An argument is usually said to be valid iff it is truth-preserving—iff it cannot be that all its premises are true and its conclusion false. But imperatives (it is normally thought) are not truth-apt. They are not in the business of saying how the world is, and therefore cannot either succeed or fail in doing so. To solve this problem, we need to find a new criterion of validity, and I aim to propose such a criterion.

Cognitivism about imperatives is the thesis that sentences in the imperative mood are truth-apt: have truth values and truth conditions. This allows cognitivists to give a simple and powerful account of consequence relations between imperatives. I argue that this account of imperative consequence has counterexamples that cast doubt on cognitivism itself.

Logic is usually thought to concern itself only with features that sentences and arguments possess in virtue of their logical structures or forms. The logical form of a sentence or argument is determined by its syntactic or semantic structure and by the placement of certain expressions called “logical constants.”[1] Thus, for example, the sentences Every boy loves some girl. and Some boy loves every girl. are thought to differ in logical form, even though they share a common syntactic and semantic (...) structure, because they differ in the placement of the logical constants “every” and “some”. By contrast, the sentences Every girl loves some boy. and Every boy loves some girl. are thought to have the same logical form, because “girl” and “boy” are not logical constants. Thus, in order to settle questions about logical form, and ultimately about which arguments are logically valid and which sentences logically true, we must distinguish the “logical constants” of a language from its nonlogical expressions. (shrink)

It would seem possible in principle … to reconstruct the ordinary sentential calculus in terms of phrastics only, and then apply it to indicatives and imperatives alike simply by adding the appropriate neustics.… It might be asked how we are to know, given two premisses in different moods, in what mood the conclusion is to be. The problem of the effect upon inferences of the moods of premisses and conclusion has been ignored by logicians who have not looked beyond the (...) indicative mood, … But if, as I do, we regard the entailment-relations of ordinary logic as relations between the phrastics of sentences, the problem becomes pressing. (R. M. Hare, The Language of Morals, pp. 26–28.). (shrink)

There is as yet no settled consensus as to what makes a term a logical constant or even as to which terms should be recognized as having this status. This essay sets out and defends a rationale for identifying logical constants. I argue for a two-tiered approach to logical theory. First, a secure, core logical theory recognizes only a minimal set of constants needed for deductively systematizing scientific theories. Second, there are extended logical theories whose objectives are to systematize various (...) pre-theoretic, modal intuitions. The latter theories may recognize a variety of additional constants as needed in order to formalize a given set of intuitions. (shrink)

We consider a paradox involving indicative conditionals (‘ifs’) and deontic modals (‘oughts’). After considering and rejecting several standard options for resolv- ing the paradox—including rejecting various premises, positing an ambiguity or hidden contextual sensitivity, and positing a non-obvious logical form—we offer a semantics for deontic modals and indicative conditionals that resolves the paradox by making modus ponens invalid. We argue that this is a result to be welcomed on independent grounds, and we show that rejecting the general validity of modus (...) ponens is compatible with vindicating most ordinary uses of modus ponens in reasoning. (shrink)

Hans Kelsen is considered by many to be the foremost legal thinker of the twentieth century. During the last decade of his life he was working on what he called a general theory of norms. Published posthumously in 1979 as Allgemeine Theorie der Normen, the book is here translated for the first time into English. Kelsen develops his "pure theory of law" into a "general theory of norms", and analyzes the applicability of logic to norms to offer an original and (...) extreme position which some have called "normative irrationalism". Examining the views of over 200 philosophers and legal theorists on law, morality, and logic, and revising several of his own earlier positions, Kelsen's final work is a mandatory resource for legal and moral philosophers. (shrink)

The question, "Which modal logic is the right one for logical necessity?," divides into two questions, one about model-theoretic validity, the other about proof-theoretic demonstrability. The arguments of Halldén and others that the right validity argument is S5, and the right demonstrability logic includes S4, are reviewed, and certain common objections are argued to be fallacious. A new argument, based on work of Supecki and Bryll, is presented for the claim that the right demonstrability logic must be contained in S5, (...) and a more speculative argument for the claim that it does not include S4.2 is also presented. (shrink)

Negative facts get a bad press. One reason for this is that it is not clear what negative facts are. We provide a theory of negative facts on which they are no stranger than positive atomic facts. We show that none of the usual arguments hold water against this account. Negative facts exist in the usual sense of existence and conform to an acceptable Eleatic principle. Furthermore, there are good reasons to want them around, including their roles in causation, chance-making (...) and truth-making, and in constituting holes and edges. (shrink)

Peter van Inwagen ’s argument for incompatibilism uses a sentential operator, “N”, which can be read as “No one has any choice about the fact that....” I show that, given van Inwagen ’s understanding of the notion of having a choice, the argument is invalid. However, a different interpretation of “N” can be given, such that the argument is clearly valid, the premises remain highly plausible, and the conclusion implies that free will is incompatible with determinism.

Peter van Inwagen has presented a compelling argument for the incompatibility of free will and determinism, which he calls “the Consequence Argument.” This argument depends on a controversial inference rule, “rule beta,” which says.

From a philosophical standpoint, the work presented here is based on van Fraassen [26]. The bulk of that paper is organized around a series of arguments against the assumption, built into standard deontic logic, that moral dilemmas are impossible; and van Fraassen only briefly sketches his alternative approach. His paper ends with the conclusion that “the problem of possibly irresolvable moral conflict reveals serious flaws in the philosophical and semantic foundations of ‘orthodox’ deontic logic, but also suggests a rich set (...) of new problems and methods for such logic.” My goal has been to suggest that some of these methods might be found in current research on nonmonotonic reasoning, and that some of the problems may have been confronted there as well.I have shown that nonmonotonic logics provide a natural framework for reasoning about moral dilemmas, perhaps even more useful than the ordinary modal framework, and that the issues surrounding the treatment of exceptional information within these logics run parallel to some of the problems posed by conditional oughts. However, there is also another way in which deontic logic might benefit from a connection to nonmonotonic reasoning. A familiar criticism among ethicists of work in deontic logic is that it is too abstract, and too far removed from the kind of problems confronted by real agents in moral deliberation. It must be said that similar criticisms of abstraction and irrelevance are often lodged against work in nonmonotonic reasoning by more practically minded researchers in artificial intelligence; but here, at least, the criticisms are taken seriously. Nonmonotonic logic aims at a qualitative account of commonsense reasoning, which can be used to relate planning and action to defeasible goals and beliefs; and at least some of the theories developed in this area have been tested in realistic situations. By linking the subject of deontic logic to this research, it may be possible also to relate the idealized study of moral reasoning typical of the field to a more robust treatment of practical deliberation. (shrink)

The book presents a theory of illocutionary acts. It argues that the study of speech acts initiatied by Austin complements the truth theoretic approach to speaker meaning. It is shown that there are aspects of speaker meaning which cannot be explained by truth theoretic approaches. Though the nature of a speech act is partially determined by the semantic type of the the sentence uttered the speaker's intention and context of utterance are important also.

Properly universal prescriptions (necessary in analysis of value-judgments) entail past-tense imperatives. does the unusability of the latter rule out the former? no, because there are many usable rules which entail past-tense imperatives. else we could not point to past breaches when teaching the rule, which remains the same throughout the teaching process, or punish for past breaches of the same rule which is still in force. similar problem about imperatives in other than the second person succumbs to kenny's distinction between (...) directives and fiats and that between different senses of 'the person commanded'. (shrink)

(1) modal logic is not needed, Since there are alternative accounts of modality. (2) modal logic does not function as logic even in the thinking of its advocates, As is revealed, E.G., When the semantics of modal logic is presented in an extensional metalanguage. Furthermore, (3) when a wider view is taken, One sees that modal logic treats as logical constants expressions that belong to a large and open syntactic class, Unlike other logical constants. Finally, (4) modal logic treats as (...) sentential operators devices that function in natural language as underlying predicates. The last two points also indicate that a theory of modality making use of modal predicates is to be preferred to an account that explains away modality in terms of quantification over possible worlds. (shrink)

The author contends that moral utterances and imperatives have different logical features. He discusses r m hare's "language of morals" in terms of his distinction between plain imperatives and deontic utterances. (staff).