This paper argues for contrastivism about the deontic modals, 'ought', 'must', and 'may'. A simple contrastivist semantics that predicts the desired entailment relations among these modals is offered.

A collection of all but two of the author's philosophical essays and lectures originally published or presented before August 1976.

This paper develops a compositional, type-driven constraint semantic theory for a fragment of the language of subjective uncertainty. In the particular application explored here, the interpretation function of constraint semantics yields not propositions but constraints on credal states as the semantic values of declarative sentences. Constraints are richer than propositions in that constraints can straightforwardly represent assessments of the probability that the world is one way rather than another. The richness of constraints helps us model communicative acts in essentially the (...) same way that we model agents’ credences. Moreover, supplementing familiar truth-conditional theories of epistemic modals with constraint semantics helps capture contrasts between strong necessity and possibility modals, on the one hand, and weak necessity modals, on the other. (shrink)

In his original semantics for counterfactuals, David Lewis presupposed that the ordering of worlds relevant to the evaluation of a counterfactual admitted no incomparability between worlds. He later came to abandon this assumption. But the approach to incomparability he endorsed makes counterintuitive predictions about a class of examples circumscribed in this paper. The same underlying problem is present in the theories of modals and conditionals developed by Bas van Fraassen, Frank Veltman, and Angelika Kratzer. I show how to reformulate all (...) these theories in terms of lower bounds on partial preorders, conceived of as maximal antichains, and I show that treating lower bounds as cutsets does strictly better at capturing our intuitions about the semantics of modals, counterfactuals, and deontic conditionals. (shrink)

According to a naive view sometimes apparent in the writings of moral philosophers, 'ought' often expresses a relation between agents and actions—the relation that obtains between an agent and an action when that action is what that agent ought to do. It is not part of this naive view that 'ought' always expresses this relation—adherents of the naive view are happy to allow that 'ought' also has an evaluative sense, on which it means, roughly, that were things ideal, some proposition (...) would be the case. What is important to the naive view is that there is also a deliberative sense of 'ought', on which it relates agents to actions. In contrast, logically and linguistically sophisticated philosophers have typically rejected this naive view. According to them, there is no argument-place for an agent in any relation expressed by 'ought', nor is there any argument-place for an action. According to this view, if Jim ought to jam, that is not because there is a special distinctive deliberative ought relation between Jim and jamming; rather, it is because a certain proposition ought to be the case: namely, that Jim jams. This essay defends the naive view, by first arguing that there are two distinct normative senses of 'ought', which actually exhibit different syntactic behavior, and then going on to argue that the deliberative sense of 'ought' relates agents to actions, rather than to propositions. It closes by drawing lessons for a range of issues in moral theory. (shrink)

According to a naïve view sometimes apparent in the writings of moral philosophers, ‘ought’ often expresses a relation between agents and actions – the relation that obtains between an agent and an action when that action is what that agent ought to do. It is not part of this naïve view that ‘ought’ always expresses this relation – on the contrary, adherents of the naïve view are happy to allow that ‘ought’ also has an epistemic sense, on which it means, (...) roughly, that some proposition is likely to be the case, and adherents of the naïve view are also typically happy to allow that ‘ought’ also has an evaluative sense, on which it means, roughly, that were things ideal, some proposition would be the case.1 What is important to the naïve view is not that these other senses of ‘ought’ do not exist, but rather that they are not exhaustive – for what they leave out, is the important deliberative sense of ‘ought’, which is the central subject of moral inquiry about what we ought to do and why – and it is this deliberative sense of ‘ought’ which the naïve view understands to express a relation between agents and actions.2 In contrast, logically and linguistically sophisticated philosophers – with a few notable exceptions3 – have rejected this naïve view. According to a dominant perspective in the interpretation of deontic logic and in linguistic semantics, for example, articulated by Roderick Chisholm (1964) and Bernard Williams (1981) in philosophy and in the dominant paradigm in linguistic semantics as articulated in particular by.. (shrink)

The existing literature treats of several investigations with a certain bearing on the question which is roughly indicated by the title “Imperatives and Logic.” Some of those investigations, however, are entirely outside the scope of the present work.Mally sets himself the task of developing a “Logik des Willens” constituting a parallel to the usual logic, the “Logik des Denkens". In order to emphasize its independence, the author also calls this “Logik des Willens” “Deontik”, and he conceives it as being based (...) on the “Wesensgesetze” of will in the same way as the usual logic is conceived as being based on the “Wesensgesetze” of thought. The author develops a formalistic deductive system on the basis of 5 axioms of demands, including the axiom that there is at least one fact which is unconditionally demanded, and through a lengthy series of theorems he arrives at the sentence that what is unconditionally demanded is identical with what is actually the case: “was sein soll, ist Tatsache”. Similarly, the author develops a system of axioms for “right” volition, including the axiom that right volition is non-contradictory. (shrink)

This volume is devoted to Lewis's work in ethics and social philosophy. Topics covered include the logic of obligation and permission; decision theory and its relation to the idea that beliefs might play the motivating role of desires; a subjectivist analysis of value; dilemmas in virtue ethics; the problem of evil; problems about self-prediction; social coordination, linguistic and otherwise; alleged duties to rescue distant strangers; toleration as a tacit treaty; nuclear warfare; and punishment. This collection, and the two preceding volumes, (...) will disseminate more widely the work of an eminent and influential contemporary philosopher. (shrink)

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.

In this paper I offer an account of the meaning of must and can within the framework of possible worlds semantics. The paper consists of two parts: the first argues for a relative concept of modality underlying modal words like must and can in natural language. I give preliminary definitions of the meaning of these words which are formulated in terms of logical consequence and compatibility, respectively. The second part discusses one kind of insufficiency in the meaning definitions given in (...) the first part, which arise from the ex falso quodlibet paradox of logical consequence. In stepwise fashion, I make an attempt to avoid most of the consequences of this paradox for the meaning definitions of must and can. (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)

This paper develops an informal semantics for 'ought to be' and 'ought to be given...' and argues for its plausibility. A feature of the semantics is that it invalidates 'if a entails b, And o(a), Then o(b)' and 'if o(a) & o(b), Then o(a&b)', While validating detachment for conditional obligation.

This paper advances a reductive semantics for ‘ought’ and a naturalistic theory of normativity. It gives a unified analysis of predictive, instrumental, and categorical uses of ‘ought’: the predictive ‘ought’ is basic, and is interpreted in terms of probability. Instrumental ‘oughts’ are analyzed as predictive ‘oughts’ occurring under an ‘in order that’ modifer (the end-relational theory). The theory is then extended to categorical uses of ‘ought’: it is argued that they are special rhetorical uses of the instrumental ‘ought’. Plausible conversational (...) principles explain how this end-relational ‘ought’ can perform the expressive functions of the moral ‘ought’. The notion of an ‘ought-simpliciter’ is also discussed. (shrink)

The crucial feature of obligation sentences to which the puzzles point is that such sentences, and evaluative sentences more generally, are defeasible. They may be warranted, given some information, only to be defeated by further information. A theory that recognizes this no longer needs to see conditional obligation as anything more than a simple combination of unary obligation and the conditional.

The article proposes an analysis of imperatives and possibility and necessity statements that (i) explains their differences with respect to the licensing of free choice any and (ii) accounts for the related phenomena of free choice disjunction in imperatives, permissions, and statements. Any and or are analyzed as operators introducing sets of alternative propositions. Free choice licensing operators are treated as quantifiers over these sets. In this way their interpretation can be sensitive to the alternatives any and or introduce in (...) their scope. (shrink)

Here is an important new theory of human action, a theory that assumes actions are founded on choices made by agents who face an open future.

A textbook on modal logic, intended for readers already acquainted with the elements of formal logic, containing nearly 500 exercises. Brian F. Chellas provides a systematic introduction to the principal ideas and results in contemporary treatments of modality, including theorems on completeness and decidability. Illustrative chapters focus on deontic logic and conditionality. Modality is a rapidly expanding branch of logic, and familiarity with the subject is now regarded as a necessary part of every philosopher's technical equipment. Chellas here offers an (...) up-to-date and reliable guide essential for the student. (shrink)

In this paper, I apply the "conceptual role semantics" approach that I have proposed elsewhere (according to which the meaning of normative terms is given by their role in practical reasoning or deliberation) to the meaning of the term 'ought'. I argue that this approach can do three things: It can give an adequate explanation of the special connection that normative judgments have to practical reasoning and motivation for action. It can give an adequate account of why the central principles (...) of deontic logic are correct. It can give an explanation of the precise ways in which the term 'ought' is systematically context-sensitive, so that the term expresses different (but systematically related) concepts in different contexts. (shrink)

When I tell you that it’s raining, I describe a way the world is—viz., rainy. I say something whose truth turns on how things are with the weather in the world. Likewise when I tell you that the weatherman thinks that it’s raining. Here the truth of what I say turns on how things are with the weatherman’s state of mind in the world. Likewise when I tell you that I think that it’s raining. Here the truth of what I (...) say turns on how things are with my state of mind in the world. (shrink)

This paper concerns what might be called the variably bad behavior of the word or. As is well known, there are a variety of environments in which the word or misbehaves – misbehaves, in the sense that it gives rise to interpretations which are not expected given the standard analysis of this word as, roughly, set union. One of these environments is the scope of a modal. This case has received a lot of attention recently in the literature, and a (...) number of researchers, including myself, have proposed accounts of or which explain its behavior in this environment. (shrink)

Conditional sentences with quantifying expressions are systematically ambigous. In one reading, the if -clause restricts the domain of the overt quantifier; in the other, the if -clause restricts the domain of a covert quantifier, which defaults to epistemic necessity. Although the ambiguity follows directly from the Lewis- Kratzer line on if, it is not generally acknowledged, which has led to pseudoproblems and spurious arguments.