'Ought' Does Not Imply 'Can'

Analysis, 2016

premisses that (i) 'T' refers (only) to T and (ii) T contains 'is true' and hence states an alethic fact. That is sufficient information to build the dependency graph and conclude that T does not depend on any non-alethic fact and hence is ungrounded. Exactly the same goes for L and C, with the usual paradoxical consequences. Given that (i) 'L' refers (only) to L and (ii) L contains 'is true' and hence states an alethic fact, we can build L's dependency graph and determine, A-decidably, that it contains only alethic nodes. So, A-decidably, L is not grounded by any non-alethic fact and hence, by (TM), is not true. It is A-decidable that L is not true. (Exactly the same reasoning applies to C.) Then L is assertible and apt for inclusion in standard logical reasoning. But that reasoning quickly leads to absurdity: we can assert the Liar equivalence (L is true iff it is not true), from which it follows that L is both true and not true. The paradox has not been blocked. 5. Conclusion I've argued that we can, in certain cases, draw clear, A-decidable conclusions about a sentence's alethic dependencies. From clear facts about a sentence's syntax and reference of its terms, we can build dependency graphs (Section 3) and reason about a sentence's dependencies. In particular, we can determine, A-decidably, that L is ungrounded, hence not true; but this quickly results in absurdity. So, A-decidably, we must reject Barker's proposal.

Every adequate semantics for conditionals and deontic "ought" must offer a solution to the miners paradox about conditional obligations. Kolodny and MacFarlane have recently argued that such a semantics must reject the validity of modus ponens. I demonstrate that rejecting the validity of modus ponens is inessential for an adequate solution to the paradox

Trends in Logic, 1997

Trends in Logic is a bookseries covering essentially the same area as the journal Studia Logicathat is, contemporary formal logic and its applications and relations to other disciplines. These include artificial intelligence, informatics, cognitive science, philosophy of science, and the philosophy of language. However, this list is not exhaustive, moreover, the range of applications, comparisons and sources of inspiration is open and evolves over time.

Survey talk delivered to the Cambridge Meta-Ethics group in 2011. After some brief remarks on the ambiguities in Hume's version of No-Ought-From-Is, I outline Prior's paradox and discuss the various responses, principally mine (the New Zealand Plan) and Schurz's (the Austrian Plan). In this text I add seven appendices drawn mainly from my introduction to Hume On Is and Ought, amplifying the argument, discussing matters arising and outlining rival approaches to the problem, principally the relevantist solution, due to Ed Mares, and the Inference Barrier solution (the Scottish/Australian Plan) due to Gillian Russell and Greg Restall. I also discuss the work of Stephen Maitzen and Mark Nelson. In this talk I emphasize the logical aspects of the issue. Drafts of my contributions to this debate available above in 'Papers'. 'The Triviality of Hume's Law', 'Coda: Truth and Consequences' and 'Subtance, Taxonomy, Content and Consequence' emphasize the logical and meta-ethical aspects of the the issue, whilst 'Letter From a Gentleman' and 'Snare's Puzzle/Hume's Purpose' emphasize meta-ethics and the historical Hume. 'Comments on "Hume's Master Argument"' deals with all three themes. The kick-off paper is 'Logic and the Autonomy of Ethics' (1989). The last in the sequence is 'Hume on is and Ought: Logic Promises and the Duke of Wellington'.

Deontic Modality, 2016

This essay offers an account of the truth conditions of sentences involving deontic modals like 'ought', designed to capture the difference between objective and subjective kinds of 'ought' This account resembles the classical semantics for deontic logic: according to this account, these truths conditions involve a function from the world of evaluation to a domain of worlds (equivalent to a so-called "modal base"), and an ordering of the worlds in such domains; this ordering of the worlds itself arises from two further elementsa probability function and a value functionsince this ordering ranks the worlds in accordance with the expected value of certain propositions that are true at those worlds. Thus, a proposition of the form 'Ought (p)' is true at a world of evaluation w if and only if p is true at all the top-ranked worlds in the domain assigned to w. This domain of worlds consists of metaphysically possible worlds, while the probability function is defined over a space of epistemically possible worlds (which may include metaphysically impossible worlds, such as worlds where Hesperus is not Phosphorus). Evidence is given that this account assigns the correct truth conditions to a wide range of sentences involving 'ought'. Since these truth conditions involve both a domain of metaphysically possible worlds and a space of epistemically possible worlds, there are two corresponding kinds of conditional involving 'ought', depending on which space of worlds is restricted by the conditional. Finally, some objections that might be raised against this account are answered.

This essay investigates the possibility of analysingì ought to do a' asìt ought to be that i do a' in an axiological setting. Axiological conceptions of deontic logic dene what ought to be as that which is better than the alternative, and dene what an agent ought to do as that which has the best outcome. How one might determine thèbest outcome' is takes philosophical work. The formal semantics for ought-to-be interprets propositions as sets of states, and the outcomes of actions for ought-to-do are also interpreted as sets of states. Thus both terms require a relation which compares sets of states based on a fundamental (weak) betterness relation between states. In this paper the relationships between ve denitions of ought-to-do and one (traditional) denition of ought-to-be are considered in such an axiological setting. It is shown that on four of those denitions it is impossible to nd a relation on sets of states which allowsì ought to do a' to be analysed asìt ought to be that i do a'. One denition of ought-to-do does make the reduction possible, but it is argued that it is defective as an interpretation of ought-to-do. Connections with Horty's work on agency and deontic logic are also discussed.

Journal of Moral Philosophy, 2019

My paper has two aims: to underscore the importance of differently time-indexed ‘ought implies can’ principles, and to apply this to the culpable inability problem. Sometimes we make ourselves unable to do what we ought, but in those cases, we may still fail to do what we ought. This is taken to be a serious problem for synchronic ‘ought implies can’ principles, with a simultaneous ‘ought’ and ‘can.’ Some take it to support diachronic ‘ought implies can,’ with a potentially temporally distinct ‘ought’ and ‘can.’ I will argue that this problem is not avoided by diachronic ‘ought implies can.’

Noûs, 1974

This paper is the beginning of an explication of the "normative-descriptive" or "ought-is" distinction by way of the notion that our knowledge of other minds is the result of our imposition of constraints on the interpretation of events as actions by agents. My hope is that a general theory of rationality and the normative can be derived from an examination of the constraints it is rational to impose on agent-interpretation, i.e., of the fundamental knowledge we have of persons as persons. My attempt at an explication of the "ought-is" distinction takes the following form: I want to find an absolutely general way of determining when "ought"-sentences are true. Since the extensions of the account given below to interesting cases of "ought"-sentences such as moral and prudential cases depend on relatively complicated constraints on agent-interpretation,l this paper will deal only with the simplest case of "ought"-sentences, the "logical ought". If logic is thought of as a normative science of belief, it yields one of the simplest cases of the "normative-descriptive" dichotomy. By the "logical ought" I understand what might be called consequences of the canons of obedience to the laws of thought. An instance of such an "ought" occurs in "If you believe that frogs are green, you ought to believe that anything that's not green is not a frog." The "logical ought" is, as it were, the minimal rational "ought", the one that prescribes closure of belief under logical consequence and proscribes inconsistency of belief. It should be pointed out that the principles of the "logical ought" often come into conflict with other canons of rationality, just as principles of moral "oughts" come into conflict with each other. The example above is surely true even if NOUS 8 (1974) ?) 1974 by Indiana University 233

Logique et Analyse

Studia Philosophiae Christianae, 2018

Bernard Williams in his essay Ought and moral obligation (OMO) takes a stand on the proper logical interpretation of ‘ought’ sentences. He claims that ought being central to ethical reflection, that is, ought issuing personal requirements to agents, is to be interpreted like any ordinary ‘ought’ – as a propositional operator that is not indexed to a person. The driving idea behind Williams’s logical point about ‘ought’ seems to be that logical interpretation of ‘ought’ sentences with moral content in terms of indexed ought lacks semantic significance. John Broome disagrees. In a series of his recent writings devoted to an analysis of the notion of normative ought, he defends the view opposite to the one fostered by Williams. According to Broome, indexation of ‘ought’ to agent matters for extra-logical reasons; it is a way of exhibiting that ought has its normative owner, which in turn is important for determining the holder of responsibility for the ought in question. In the paper I argue that Broome may be right, but his arguments do not show that fact. In particular, I claim that he is wrong in thinking that indexation in terms of ownership is useful in the analysis of ‘ought’ sentences with agentive content, and thus nicely applies to moral ought being a paradigmatic example of such sentences. According to my diagnosis, Broome’s positive view about the semantic and ethical significance of interpreting agentive ought as indexed ought, suffers from one central problem. It alludes to an unsuccessful substantive semantics of ‘indexed ought’ that fails to give an accurate explanation of the meaning of the ought in question. I conclude the paper by offering an alternative to Broome’s substantive semantics of ‘indexed ought’, and explain why I think that it fares better in capturing the nature of the agentive ought.