The actualism/possibilism debate in ethics is about whether counterfactuals of freedom concerning what an agent would freely do if they were in certain circumstances even partly determines that agent’s obligations. This debate arose from an argument against the coherence of utilitarianism in the deontic logic literature. In this chapter, we first trace the historical origins of this debate and then examine actualism, possibilism, and securitism through the lens of consequentialism. After examining their respective benefits and drawbacks, we argue (...) that, contrary to what has been assumed, actualism and securitism both succumb to the so-called nonratifiability problem. In making this argument, we develop this problem in detail and argue that it’s a much more serious problem than has been appreciated. We conclude by arguing that an alternative view, hybridism, is independently the most plausible position and best fits with the nature of consequentialism, partly in light of avoiding the nonratifiability problem. (shrink)

‘Possibilist Explanation’ is a promising account of scientific explanation which avoids the familiar problems of “how-possibly explanations”. It explains an event by showing how-actually it was epistemically possible, instead of why it was epistemically necessary. Its explanandum is the epistemic possibility of an actual event previously considered epistemically impossible. To define PE, two new concepts are introduced: ‘permissive condition’ and ‘possibilist law’. A permissive condition for an event is something that does not entail the event itself, but a necessary condition (...) for it. A ‘Possibilist Law’ is a kind of scientific law that predicts that in the absence of a necessary condition N, the event E is not possible. Both PE and PL are legitimate and neglected parts of scientific knowledge and are especially suitable for human sciences. (shrink)

Climate scientists frequently employ heavily idealized models. How should these models be interpreted? Some philosophers have advanced a possibilist interpretation: climate models stand in for possible scenarios that could occur, but do not provide information about how probable those scenarios are. The present paper argues that possibilism is (a) undermotivated, (b) incompatible with successful practices in the science, and (c) unable to correct for known biases. The upshot is that the models should be interpreted probabilistically in at least some (...) cases. (shrink)

How is what an agent ought to do related to what an agent ought to prefer that she does? More precisely, suppose we know what an agent’s preference ordering ought to be over the prospects of performing the various courses of action open to her. Can we infer from this information how she ought to act, and if so, how can we infer it? One view (which, for convenience, I will call ‘actualism’) is that an agent ought to  just (...) in case she ought to prefer the prospect of her -ing to the prospect of her not -ing. Another view (which, for convenience, I will call ‘possibilism’) is that an agent ought to  just in case she ought to prefer the prospect of some maximally specific option that involves her -ing to the prospect of any maximally specific option that does not involve her -ing (with the quantifiers appropriately restricted). After making some preliminary clarifications in part 1, I will discuss actualism and possibilism in parts 2 and 3, respectively. I will argue, in part 2, that actualism is very far from the truth. And I will argue, in part 3, that while the standard version of possibilism faces significant problems, there are much better versions of possibilism that avoid the objections to the standard view. Ultimately, however, I will argue that even the best forms of possibilism are not acceptable. Then, in part 4, I will propose what I take to be the best view, one that is neither strictly possibilist nor actualist, and that avoids the shortcomings of both these views. (shrink)

Hierarchical models are commonly used for modelling uncertainty. They arise whenever there is a `correct' or `ideal' uncertainty model but the modeller is uncertain about what it is. Hierarchical models which involve probability distributions are widely used in Bayesian inference. Alternative models which involve possibility distributions have been proposed by several authors, but these models do not have a clear operational meaning. This paper describes a new hierarchical model which is mathematically equivalent to some of the earlier, possibilistic models and (...) also has a simple behavioural interpretation, in terms of betting rates concerning whether or not a decision maker will agree to buy or sell a risky investment for a specified price. We give a representation theorem which shows that any consistent model of this kind can be interpreted as a model for uncertainty about the behaviour of a Bayesian decision maker. We describe how the model can be used to generate buying and selling prices and to make decisions. (shrink)

An account of non-existing objects called 'classical possibilism', according to which objects that don't actually exist do exist in various other ways, is implemented in a two-dimensional modal logic with non-traditional predication theory. This account is very similar to Priest's, but preserves bivalence and does not endorse dialethism. The power of classical possibilism is illustrated by giving some examples that makes use of a description theory of reference. However, the same effect could also be achieved in a more (...) Millian fashion. It is argued that classical possibilism is ontologically more neutral than is commonly thought, because it allows for the formulation of various forms of reductionism within the object language. (shrink)

There has been considerable debate regarding the relative merits of two theses about moral obligation known as actualism and possibilism. Both theses seek to give expression to the general idea that one ought to do the best one can. According to actualism, one’s obligations turn on what would happen if one chose some course of action, whereas, according to possibilism, they turn on what could happen if one chose some course of action. There are two strands to the (...) debate: the substantive verdicts that the two theses render in particular cases, and the accounts that they yield of the conceptual structure of moral obligation. Possibilism is conceptually appealing, whereas actualism is not, but the latter may seem to render superior substantive verdicts. In this paper, it is argued that, by turning from the objectivist’s emphasis on what is actually best to the prospectivist’s emphasis on what one’s evidence indicates is best, possibilists can provide an account of moral obligation that is both conceptually and substantively attractive. (shrink)

Possibilistic states of information are fuzzy sets of possible worlds. They constitute a complete lattice, which can be endowed with a monoidal operation (a t-norm) to produce a quantal. An algebraic semantics is presented which links possibilistic formulae with information states, and gives a natural interpretation of logical connectives as operations on fuzzy sets. Due to the quantal structure of information states, we obtain a system which shares several features with (exponential-free) intuitionistic linear logic. Soundness and completeness are proved, parametrically (...) on the choice of the t-norm operation. (shrink)

In this extended critical discussion of 'Kant's Modal Metaphysics' by Nicholas Stang (OUP 2016), I focus on one central issue from the first chapter of the book: Stang’s account of Kant’s doctrine that existence is not a real predicate. In §2 I outline some background. In §§3-4 I present and then elaborate on Stang’s interpretation of Kant’s view that existence is not a real predicate. For Stang, the question of whether existence is a real predicate amounts to the question: ‘could (...) there be non-actual possibilia?’ (p.35). Kant’s view, according to Stang, is that there could not, and that the very notion of non-actual or ‘mere’ possibilia is incoherent. In §5 I take a close look at Stang’s master argument that Kant’s Leibnizian predecessors are committed to the claim that existence is a real predicate, and thus to mere possibilia. I argue that it involves substantial logical commitments that the Leibnizian could reject. I also suggest that it is danger of proving too much. In §6 I explore two closely related logical commitments that Stang’s reading implicitly imposes on Kant, namely a negative universal free logic and a quantified modal logic that invalidates the Converse Barcan Formula. I suggest that each can seem to involve Kant himself in commitment to mere possibilia. (shrink)

A recent ontological variant of Cramer’s Transactional Interpretation, called “Possibilist Transactional Interpretation” or PTI, is extended to the relativistic domain. The present interpretation clarifies the concept of ‘absorption,’ which plays a crucial role in TI (and in PTI). In particular, in the relativistic domain, coupling amplitudes between fields are interpreted as amplitudes for the generation of confirmation waves (CW) by a potential absorber in response to offer waves (OW), whereas in the nonrelativistic context CW are taken as generated with certainty. (...) It is pointed out that solving the measurement problem requires venturing into the relativistic domain in which emissions and absorptions take place; nonrelativistic quantum mechanics only applies to quanta considered as ‘already in existence’ (i.e., ‘free quanta’), and therefore cannot fully account for the phenomenon of measurement, in which quanta are tied to sources and sinks. (shrink)

Abstract‘Possibilist Explanation’ is a promising account of scientific explanation which avoids the familiar problems of “how-possibly explanations”. It explains an event by showing how-actually it was epistemically possible, instead of why it was epistemically necessary. Its explanandum is the epistemic possibility of an actual event previously considered epistemically impossible. To define PE, two new concepts are introduced: ‘permissive condition’ and ‘possibilist law’. A permissive condition for an event is something that does not entail the event itself, but a necessary condition (...) for it. A ‘Possibilist Law’ is a kind of scientific law that predicts that in the absence of a necessary condition N, the event E is not possible. Both PE and PL are legitimate and neglected parts of scientific knowledge and are especially suitable for human sciences. (shrink)

A central stream running through the history of philosophy has been the attempt to gather a wide range of ostensibly disparate intuitive phenomena under a small, integrated set of concepts. Edward Zalta’s work is a sustained celebration of this tradition. This paper — part of a symposium on Zalta's work — is a friendly, but critical examination of Zalta's commitment to possibilism and the roles they play in his theory.

A recent ontological modification of Cramer’s Transactional Interpretation, called “Possibilist Transactional Interpretation” or PTI, is extended to the relativistic domain. The present interpretation clarifies the concept of ‘absorption,’ which plays a crucial role in TI. In particular, in the relativistic domain, coupling amplitudes between fields are interpreted as amplitudes for the generation of confirmation waves by a potential absorber in response to offer waves, whereas in the nonrelativistic context CW are taken as generated with certainty. It is pointed out that (...) solving the measurement problem requires venturing into the relativistic domain in which emissions and absorptions take place; nonrelativistic quantum mechanics only applies to quanta considered as ‘already in existence’, and therefore cannot fully account for the phenomenon of measurement, in which quanta are tied to sources and sinks. (shrink)

In Modal Logic as Metaphysics, Timothy Williamson claims that the possibilism-actualism (P-A) distinction is badly muddled. In its place, he introduces a necessitism-contingentism (N-C) distinction that he claims is free of the confusions that purportedly plague the P-A distinction. In this paper I argue first that the P-A distinction, properly understood, is historically well-grounded and entirely coherent. I then look at the two arguments Williamson levels at the P-A distinction and find them wanting and show, moreover, that, when the (...) N-C distinction is broadened (as per Williamson himself) so as to enable necessitists to fend off contingentist objections, the P-A distinction can be faithfully reconstructed in terms of the N-C distinction. However, Williamson’s critique does point to a genuine shortcoming in the common formulation of the P-A distinction. I propose a new definition of the distinction in terms of essential properties that avoids this shortcoming. (shrink)

Albert Hirschman's possibilism originated from his work on development and democracy; at the same time, it offered tools for evaluating projects that Judith Tendler innovatively utilized in her professional work, where she interweaved theory and practice, methodology and ethics. Starting from observation in the field, comparisons, linkages, inverted sequences and unexpected consequences are really key elements in a type of evaluation that works toward improvement, "for a better world." The enduring vitality of the thinking of these forerunners is what (...) motivates the reconstruction of their intellectual trajectories: from the way of learning from the successes and failures of programs, to how to deal with such themes as complexity, mechanisms, uncertainty, change, that are at the core of current debates. The book aims at showing both the relevance of practical work for the advancement of social theory, and the need for a theoretical attitude - based on a capacity of being surprised - for the strengthening of democratic professionalism and the attainment of sound results. It will constitute a basic reading for social scientists, decision-makers, policy implementers, evaluators and students. (shrink)

Do facts about what an agent would freely do in certain circumstances at least partly determine any of her moral obligations? Actualists answer ‘yes’, while possibilists answer ‘no’. We defend two novel hybrid accounts that are alternatives to actualism and possibilism: Dual Obligations Hybridism and Single Obligation Hybridism. By positing two moral ‘oughts’, each account retains the benefits of actualism and possibilism, yet is immune from the prima facie problems that face actualism and possibilism. We conclude by (...) highlighting one substantive difference between our two hybrid accounts. (shrink)

We introduce possibilistic beliefs into strategic games, describing a player’s belief about his opponents’ strategies as the set of their strategies he regards as possible. We formulate possibilistic strategic games where each player has preferences over his own strategies conditional on his possibilistic belief about his opponents’ strategies. We define several solution concepts for possibilistic strategic games such as (strict) equilibria, rationalizable sets, iterated elimination of never-best responses, and iterated elimination of strictly dominated strategies, and we study their properties and (...) relationships. We develop a class of possibilistic strategic games called possibilistic supermodular games to relate supermodular games to possibilistic strategic games. Lastly, we discuss a direction of extending our possibilistic framework to games with incomplete information. (shrink)

Actualism is a widely-held view in the metaphysics of modality that arises in response to the thesis of possibilism, the doctrine that, in addition to the things that actually exist — in particular, things that exist alongside us in the causal order — there are merely possible things as well, things that, in fact, fail to be actual but which could have been. The central motivation for possibilism is to explain what it is about reality that grounds such (...) intuitively true propositions as that Wittgenstein (who was childless) could have had children. In answer, possibilists argue that we must simply broaden our understanding of reality, of what there is in the broadest sense, beyond the actual, beyond what actually exists, so that it also includes the merely possible. In particular, says the possibilist, there are merely possible people, things that are not, in fact, people but which could have been. So, for the possibilist, the proposition that Wittgenstein could have had children is grounded in the fact that, among the possibilia, there are those that could have been his children. Actualism is (at the least) the denial of possibilism; to be an actualist is to deny that there are any possibilia. Put another way, for the actualist, there is no realm of reality, or being, beyond actual existence; to be is to exist, and to exist is to be actual. This article investigates the origins and nature of the debate between possibilists and actualists, with a particular focus on the implications of the debate for quantified modal logic. -/- . (shrink)

Argues (1) that the debate between actualists and possibilists in deontic logic distorts what is really at issue, and (2) that reframing the debate as being about reasons strongly suggests that those with possibilist sympathies should adopt more moderate claims (which may nevertheless be distinct from actualism).

A great deal of scholarship defines rational thought in terms of probability theory. An important problem with such an approach is that disasters, particularly large disasters, do not provide us with a meaningful distribution of events that would approximate a normal curve. Here, I propose that using possibilistic thinking can helpfully complement probabilistic thinking regarding risk and disaster. Possibilistic thinking highlights consequences of actions or events, while not ignoring their likelihood of occurrence. I point out the myriad ways that individuals (...) and organizations use possibilistic thinking, even if they do not recognized it as such. I propose several conceptual tools to help discipline a possibilistic approach. (shrink)

Possibilistic logic and modal logic are knowledge representation frameworks sharing some common features, such as the duality between possibility and necessity, and the decomposability of necessity for conjunctions, as well as some obvious differences since possibility theory is graded. At the semantic level, possibilistic logic relies on possibility distributions and modal logic on accessibility relations. In the last 30 years, there have been a series of attempts for bridging the two frameworks in one way or another. In this paper, we (...) compare the relational semantics of epistemic logics with simpler possibilistic semantics of a fragment of such logics that only uses modal formulas of depth 1. This minimal epistemic logic handles both all-or-nothing beliefs and explicitly ignored facts. We also contrast epistemic logic with the S5-based rough set logic. Finally, this paper presents extensions of generalized possibilistic logic with objective and non-nested multimodal formulas, in the style of modal logics KD45 and S5. (shrink)

In this paper I probe the idea that neither possibilism nor trivialism could be ruled out on a purely logical basis. I use the apparatus of relational structures used in the semantics for modal logics to engineer some models of possibilism and trivialism and I discuss a philosophical stance about logic, truth values and the meaning of connectives underlying such analysis.

In this article I defend a form of classical possibilism with an actualist foundation. As a matter of fact, I believe that this position is more in keeping with the classical metaphysical tradition. According to this form of possibilism, I construe possible objects as possible non-existing objects of an existing producing power. Consequently, they are nothing vis-à -vis the modality of their own actual being, although they do exist with regard to the modality of the producing power’s being. (...) The actualist requirement prescribed by the Frege-Quinean criterion of the quantification domain is thus fulfilled; indeed, really possible objects are not actual objects, but their possibility is actual. (shrink)

. This paper first provides a brief survey of a possibilistic handling of default rules. A set of default rules of the form, “generally, from α deduce β”, is viewed as the family of possibility distributions satisfying constraints expressing that the situation where α and β is true has a greater plausibility than the one where a and - β is true. When considering only the subset of linear possibility distributions, the well-known System P of postulates proposed by Kraus, Lehmann (...) and Magidor, has been obtained. We also present two rational extensions: one based on the minimum specificity principle and the other is based on the lexicographic ordering. The second part of the paper presents an empirical study of three desirable properties for a consequence relation that capture default reasoning: Rationality, Property Inheritance and Ambiguity Preservation. An experiment is conducted to investigate 13 patterns of inference for the test of these properties. Our experimental apparatus confirms previous results on the relevance of System P, and enforces the psychological relevance of the studied properties. (shrink)

This paper first provides a brief survey of a possibilistic handling of default rules. A set of default rules of the form, "generally, from α deduce β", is viewed as the family of possibility distributions satisfying constraints expressing that the situation where α and β is true has a greater plausibility than the one where α and ⇁β is true. When considering only the subset of linear possibility distributions, the well-known System P of postulates proposed by Kraus, Lehmann and Magidor, (...) has been obtained. We also present two rational extensions: one based on the minimum specificity principle and the other is based on the lexicographic ordering. The second part of the paper presents an empirical study of three desirable properties for a consequence relation that capture default reasoning: Rationality, Property Inheritance and Ambiguity Preservation. An experiment is conducted to investigate 13 patterns of inference for the test of these properties. Our experimental apparatus confirms previous results on the relevance of System P, and enforces the psychological relevance of the studied properties. (shrink)

The actualism/possibilism debate in ethics is traditionally formulated in terms of whether true counterfactuals of freedom about the future (true subjunctive conditionals concerning what someone would freely do in the future if they were in certain circumstances) even partly determine an agent's present moral obligations. But the very assumption that there are true counterfactuals of freedom about the future conflicts with the idea that freedom requires a metaphysically open future. We develop probabilism as a solution to the actualism/possibilism (...) debate, a solution that accommodates an open future requirement for freedom. We argue that probabilism resolves the conflicting intuitions that arise between actualists and possibilists and maintains certain distinct advantages over actualism and possibilism. (shrink)

There is a heated dispute among consequentialists concerning the following deontic principle.

Description Logics (DLs) are a family of formal knowledge representation formalisms and the most well-known formalisms in semantics-based systems. The central focus of this research is on logical-terminological characterisation/analysis of possibilistic and probabilistic descriptions of events in DLs. Based on a logical characterisation of the concept of `being', this paper conceptualises events within DLs world descriptions. Accordingly, it deals with the concepts of `possibility of events' and `probability of events'. The main goal of this research is to investigate how possible (...) and probable notations can, terminologically and logically, be interpreted and analysed within DLs world descriptions. In other words, the research logically-terminologically investigates how possibilistic and probabilistic descriptions of events can be expressed in DLs. (shrink)

The paper presents a ‘multiple agent’ logic where formulas are pairs of the form, made of a proposition and a subset of agents. The formula is intended to mean ‘ all agents in believe that is true’. The formal similarity of such formulas with those of possibilistic logic, where propositions are associated with certainty levels, is emphasised. However, the subsets of agents are organised in a Boolean lattice, while certainty levels belong to a totally ordered scale. The semantics of a (...) set of ‘multiple agent’ logic formulas is expressed by a mapping which associates a subset of agents with each interpretation. Soundness and completeness results are established. Then a joint extension of the multiple agent logic and possibilistic logic is outlined. In this extended logic, propositions are then associated with both sets of agents and certainty levels. A formula then expresses that ‘all agents in set believe that is true at least at some level’. The semantics is then given in terms of fuzzy sets of agents that find an interpretation more or less possible. A specific feature of possibilistic logic is that the inconsistency of a knowledge base is a matter of degree. The proposed setting enables us to distinguish between the global consistency of a set of agents and their individual consistency. In particular, given a set of multiple agent possibilistic formulas, one can compute the subset of agents that are individually consistent to some degree. (shrink)

The expressive power of logic is believed to be able to model most of the fundamental aspects of information retrieval. However, it is also understood that classical logic is ineffective for handling partiality and uncertainty in IR. Applying non-classical logics such as the AGM belief revision logic and the possibilistic logic to adaptive information retrieval is appealing since they provide a powerful and rigorous framework to model partiality and uncertainty inherent in any IR processes. The maxi-adjustment method, which is an (...) effective computational apparatus of the AGM paradigm, is applied to develop the learning components of the adaptive information agents. Essentially, maxi-adjustment allows the partial representation K of a user's information needs N to be refined gradually based on the user's relevance feedback t. Generally speaking, learning in adaptive information agents is characterised by the AGM belief revision Kt*. On the other hand, possibilistic logic supports a gradated assessment of the uncertainty arising from matching K with the imperfect characterisation d of an information object D. Information matching in adaptive information agents is underpinned by K ƕ d, where ƕ is the possibilistic inference relation. This paper illustrates how maxi-adjustment and possibilistic deduction can be applied to develop the adaptive information agents. Their impact on the agents learning autonomy and explanatory power is also discussed. (shrink)

In his book Modal Logic as Metaphysics, Williamson argues that the traditional actualist‐possibilist debate should be abandoned as hopelessly unclear and that we should get on with the clearer contingentism‐necessitism debate. We think that Williamson’s pessimism is not warranted by the brief arguments he gives. In this paper, we explain why and provide a clear formulation of the traditional actualist‐possibilist debate.

Hardy’s non-locality paradox is a proof without inequalities showing that certain non-local correlations violate local realism. It is ‘possibilistic’ in the sense that one only distinguishes between possible outcomes (positive probability) and impossible outcomes (zero probability). Here we show that Hardy’s paradox is quite universal: in any (2,2,l) or (2,k,2) Bell scenario, the occurrence of Hardy’s paradox is a necessary and sufficient condition for possibilistic non-locality. In particular, it subsumes all ladder paradoxes. This universality of Hardy’s paradox is not true (...) more generally: we find a new ‘proof without inequalities’ in the (2,3,3) scenario that can witness non-locality even for correlations that do not display the Hardy paradox. We discuss the ramifications of our results for the computational complexity of recognising possibilistic non-locality. (shrink)