Temporal Logic

The article reviews some analyses of temporal language in logical approaches to natural language semantics. It considers some asymmetries between past and future, manifested in language, which motivate the “standard view” of the non-reversibility of time and the persistence of the past. It concludes with a puzzle about the changing past which challenges the standard view.

Philosophical views about the logical structure of time are typically divided between proponents of A and B theories, based on McTaggart's A and B series. Drawing on Paul Ricoeur's hermeneutic phenomenology, I develop and defend McTaggart's thesis that the C series and the A series working together give a consistent description of temporal experience, provided that the two series are treated as distinct dimensions internal to time. In the proposed two-dimensional model, the C series expresses a nesting order of the (...) constitutive states of a world, whereas ontological continuity and change are properties of the A series. This, I argue, allows for limited backward causation. (shrink)

This paper presents the proof of the apparent nature of relative simultaneity originally derived from Einstein’s Special Theory of Relativity (STR). The proof does not challenge the validity of the STR but uncovers fundamental and widespread error in understanding of practical implications of Lorentz transformations. It is demonstrated that more than a century long debates generally miss the point. This results in counterintuitive claims of coexisting multiple time realities by mere equivalence of equal clock indications and simultaneity. Such claims have (...) little empirical significance but they are substantial in education and philosophy which has become utterly confused after universal acceptance of the STR and rejections of Henri Bergson’s challenge. There is nothing more to “relative simultaneity” other than the effect of identical clocks being shifted by an offset which depends on synchronisation method. (shrink)

The paper consists of two parts. The first critically analyses Meyer’s [2005] version of the triviality objection to presentism (according to which, presentism is either trivial or untenable), and tries to show that his argument is untenable because – contrary to what he claimed – he did not take into account the entire possible spectrum of interpretations of the presentist’s thesis. In the second, positive part of the paper, it is shown that a leading form of tensed theory of time (...) postulates the same ontology as presentism and that it avoids the triviality problem which means that it can be used to generate an alternative formulation of presentism which is no longer vulnerable to the triviality objection. (shrink)

In traditional semantics for classical logic and its extensions, such as modal logic, propositions are interpreted as subsets of a set, as in discrete duality, or as clopen sets of a Stone space, as in topological duality. A point in such a set can be viewed as a "possible world," with the key property of a world being primeness—a world makes a disjunction true only if it makes one of the disjuncts true—which classically implies totality—for each proposition, a world either (...) makes the proposition true or makes its negation true. This chapter surveys a more general approach to logical semantics, known as possibility semantics, which replaces possible worlds with possibly partial "possibilities." In classical possibility semantics, propositions are interpreted as regular open sets of a poset, as in set-theoretic forcing, or as compact regular open sets of an upper Vietoris space, as in the recent theory of "choice-free Stone duality." The elements of these sets, viewed as possibilities, may be partial in the sense of making a disjunction true without settling which disjunct is true. We explain how possibilities may be used in semantics for classical logic and modal logics and generalized to semantics for intuitionistic logics. The goals are to overcome or deepen incompleteness results for traditional semantics, to avoid the nonconstructivity of traditional semantics, and to provide richer structures for the interpretation of new languages. (shrink)

Temporal logic is of importance in theoretical computer science for its application in formal verification, to state requirements of hardware or software systems. Linear temporal logic is an appropriate logical environment to formalize Yablo’s paradox which is seemingly non-self-referential and basically has a sequential structure. We give a brief review of Yablo’s paradox and its various versions. Formalization of these paradoxes yields some theorems in Linear Temporal Logic (LTL) for which we give syntactic proofs using an appropriate axiomatization of LTL.

Gabbay's separation theorem about linear temporal logic with past has proved to be one of the most useful theoretical results in temporal logic. In this paper, we establish an analogous statement a...

We present the proof that the temporal logic of two-dimensional Minkowski spacetime is decidable, PSPACE-complete. The proof is based on a type of two-dimensional mosaic. Then, we present the modification of the proof so as to work for slower-than-light signals. Finally, a subframe of the slower-than-light Minkowski frame is used to prove the new result that the temporal logic of real intervals with during as the accessibility relation is also PSPACE-complete.

This essay narrates some of the influences that Alasdair Urquhart has had on computer science at the intersection of automated theorem proving, temporal logic and lattice theory—topics that have no obvious relationship to one another. I illustrate this by showing how Allen’s temporal relations are represented in a system for constraint logic programming over intervals and how the combination of a linear-resolution theorem prover and an interval constraint satisfaction system are connected via a lattice-theoretical semantic model. I also speculate on (...) whether some of Thich Nhat Hanh’s meditation teachings might have been one of the sources of Alasdair’s creative inspirations and preternatural capacity for lateral thinking. (shrink)

Branching time is a popular theory of time that is intended to account for the openness of the future. Generally, branching-time models the openness of the future by positing a multiplicity of concrete alternative futures mirroring all the possible ways the future could unfold. A distinction is drawn in the literature among branching-time theories: those that make use of moment-based structures and those that employ history-based ones. In this paper, I introduce and discuss a particular kind of openness relative to (...) the possibility that time ends (doomsday). I then show that whereas moment-based branching structures cannot represent this kind of openness, history-based structures can account for it. The conclusion is that history-based structures have an advantage over moment-based ones. (shrink)

This paper explores mutable futurism, the view according to which the future can literally change—that is, it can happen that a future time t changes from containing an event E to lacking it. Mutable futurism has received little attention so far, and the details and implications of the view are underexplored in the literature. For instance, it currently lacks a precise metaphysical model and a formal semantics. Although we do not endorse mutable futurism, our goal here is to strengthen the (...) case for mutable futurism and help establish it as a worthy contender in the debate on the philosophy of time. To attain this goal, we try to make mutable futurism, along with its metaphysical and inferential commitments, as clear as possible, by providing it with a coherent metaphysical model and a plausible semantics, and we show that it can be backed by theoretical reasons. (shrink)

Ewald considered tense operators G, H, F and P on intuitionistic propositional calculus and constructed an intuitionistic tense logic system called IKt. In 2014, Figallo and Pelaitay introduced the variety IKt of IKt-algebras and proved that the IKt system has IKt-algebras as algebraic counterpart. In this paper, we introduce and study the variety of tense Nelson algebras. First, we give some examples and we prove some properties. Next, we associate an IKt-algebra to each tense Nelson algebras. This result allowed us (...) to determine the congruence of the tense Nelson algebras and also to characterize the subdirectly irreducible tense Nelson algebras and particularly the simple tense Nelson algebras. Finally, we prove that there exists an equivalence between the category of IKt-algebras and the category of tense centered Nelson algebras. (shrink)

This paper articulates in formal terms a crucial distinction concerning future contingents, the distinction between what is true about the future and what is reasonable to believe about the future. Its key idea is that the branching structures that have been used so far to model truth can be employed to define an epistemic property, credibility, which we take to be closely related to knowledge and assertibility, and which is ultimately reducible to probability. As a result, two kinds of claims (...) about future contingents—one concerning truth, the other concerning credibility—can be smoothly handled within a single semantic framework. (shrink)

In epistemic logic we are not only interested in the propositional knowledge expressed by “knowing that” operators, but also care about other types of knowledge used in natural language. In [1], Plaza proposed the “knowing value” operators and gave the complete axiomatization for the logic of knowledge with nonrigid designators. Moreover, in [2] Halpern and colleagues holds that, when analyzing a system in terms of knowledge, not only is the current state of knowledge of the agents in the system relevant, (...) but also how that state of knowledge changes over time. So we introduce temporal logic operators ‘next’ and ‘until’ to extend Plaza’s system. The completeness proof is highly non-trivial and we referred to the work of [2, 3]. (shrink)

Software-controlled bots, also called social bots, are computer programs that act like human users on social media platforms. Recent work on detection of social bots is dominated by machine learning approaches. In this paper we explore bot detection as a model checking problem. We introduce Temporal Network Logic which we use to specify social networks where agents can post and follow each other. In this logic we formalize different types of social bot behavior. These are formulas that are satisfied in (...) a model of a network with bots. We provide a simple algorithm to extract a logical model from a real-life social network. We show that we can reduce TNL to a fragment of linear temporal logic with past and use this to establish the computational efficiency of model checking for social bot detection. (shrink)

As a growing area of research, the philosophy of time is increasingly relevant to different areas of philosophy and even other disciplines. This book describes and evaluates the most important debates in philosophy of time, under several subject areas: metaphysics, epistemology, physics, philosophy of language, philosophy of mind, cognitive science, rationality, and art. -/- Questions this book investigates include: Can we know what time really is? Is time possible, especially given modern physics? Must there be time because we cannot think (...) without it? What do we experience of time? How might philosophy of time be relevant to understanding the mind-body relationship or evidence in cognitive science? Can the philosophy of time help us understand biases toward the future and the fear of death? How is time relevant to art – and is art relevant to philosophical debates about time? Finally, what exactly could time travel be? And could time travel satisfy emotions such as nostalgia and regret? -/- Through asking such questions, and showing how they might be best answered, the book demonstrates the importance philosophy of time has in contemporary thought. Each of the book’s 10 chapters begins with a helpful introduction and ends with study questions and an annotated list of further readings. This and a comprehensive bibliography at the end of the book prepare the reader to go further in their study of the philosophy of time. (shrink)

This work aims to make tense logic a more robust tool for ontologists, philosophers, knowledge engineers and programmers by outlining a fusion of tense logic and ontology of time. In order to make tense logic better understandable, the central formal primitives of standard tense logic are derived as theorems from an informal and intuitive ontology of time. In order to make formulation of temporal propositions easier, temporal operators that were introduced by Georg Henrik von Wright are developed, and mapped to (...) the ontology of time. (shrink)

This book launches a sustained defense of a radical interpretation of the doctrine of the open future. Patrick Todd argues that all claims about undetermined aspects of the future are simply false.

At least since Aristotle’s famous 'sea-battle' passages in On Interpretation 9, some substantial minority of philosophers has been attracted to the doctrine of the open future--the doctrine that future contingent statements are not true. But, prima facie, such views seem inconsistent with the following intuition: if something has happened, then (looking back) it was the case that it would happen. How can it be that, looking forwards, it isn’t true that there will be a sea battle, while also being true (...) that, looking backwards, it was the case that there would be a sea battle? This tension forms, in large part, what might be called the problem of future contingents. A dominant trend in temporal logic and semantic theorizing about future contingents seeks to validate both intuitions. Theorists in this tradition--including some interpretations of Aristotle, but paradigmatically, Thomason (1970), as well as more recent developments in Belnap, et. al (2001) and MacFarlane (2003, 2014)--have argued that the apparent tension between the intuitions is in fact merely apparent. In short, such theorists seek to maintain both of the following two theses: (i) the open future: Future contingents are not true, and (ii) retro-closure: From the fact that something is true, it follows that it was the case that it would be true. It is well-known that reflection on the problem of future contingents has in many ways been inspired by importantly parallel issues regarding divine foreknowledge and indeterminism. In this paper, we take up this perspective, and ask what accepting both the open future and retro-closure predicts about omniscience. When we theorize about a perfect knower, we are theorizing about what an ideal agent ought to believe. Our contention is that there isn’t an acceptable view of ideally rational belief given the assumptions of the open future and retro-closure, and thus this casts doubt on the conjunction of those assumptions. (shrink)

ABSTRACT We critically review two extant paradigms for understanding the systematic interaction between modality and tense, as well as their respective modifications designed to do justice to the contingency of time’s structure and composition. We show that on either type of theory, as well as their respective modifications, some principles prove logically valid whose truth might sensibly be questioned on metaphysical grounds. These considerations lead us to devise a more general logical framework that allows accommodation of those metaphysical views that (...) its predecessors rule out by fiat. (shrink)

Temporaryism—the view that not always everything always exists—comes in two main versions: presentism and expansionism. Both versions of the view are commonly formulated using the notion of being present, which we, among others, find problematic. Expansionism is also sometimes accused of requiring extraordinary conceptual tools for its formulation. In this paper, we put forward systematic characterizations of presentism and expansionism which involve neither the notion of being present nor unfamiliar conceptual tools. These characterizations are full-blown logics, each logic comprising an (...) axiomatic proof system and an intuitive semantics with respect to which the system is both sound and complete. (shrink)

We defend the thesis that every necessarily true proposition is always true. Since not every proposition that is always true is necessarily true, our thesis is at odds with theories of modality and time, such as those of Kit Fine and David Kaplan, which posit a fundamental symmetry between modal and tense operators. According to such theories, just as it is a contingent matter what is true at a given time, it is likewise a temporary matter what is true at (...) a given possible world; so a proposition that is now true at all worlds, and thus necessarily true, may yet at some past or future time be false in the actual world, and thus not always true. We reconstruct and criticize several lines of argument in favor of this picture, and then argue against the picture on the grounds that it is inconsistent with certain sorts of contingency in the structure of time. (shrink)

The aim of this paper is to argue that the adoption of an unrestricted principle of bivalence is compatible with a metaphysics that (i) denies that the future is real, (ii) adopts nomological indeterminism, and (iii) exploits a branching structure to provide a semantics for future contingent claims. To this end, we elaborate what we call Flow Fragmentalism, a view inspired by Kit Fine (2005)’s non-standard tense realism, according to which reality is divided up into maximally coherent collections of tensed (...) facts. In this way, we show how to reconcile a genuinely A-theoretic branching-time model with the idea that there is a branch corresponding to the thin red line, that is, the branch that will turn out to be the actual future history of the world. (shrink)

In this article, I present a formal semantic framework that renders explicit how to reconcile the condition that a proposition about a contingent future event is true at a moment t0 with the idea that at t0, this proposition is ‘truth-maker indeterminate’: a state of affairs making it true will obtain later on, though no such state of affairs obtains at t0. The semantics I formulate employs ‘open temporal models’. They represent the passage of time by a specific component termed (...) time-resource, which acts on durations construed as model-external inputs. A model does not by itself specify which course of events gets actualized in a given duration depending on the latest moment that has already got actualized. A time-resource merely represents schematically the dependence between a moment t and a course of events that gets actualized in a time-span of a given length counted from t; until that much time has indeed passed, it is not fixed which course of events actually extends t. Further, I introduce evaluations as a fine-grained tool for studying truth-conditions of tensed formulas, and I use this tool to define the notion of truth-maker. I define what it means that a truth-maker will obtain but does not, and what it means for a truth-maker to be determinate. It is proven that my semantic analysis retains the desirable link between determinacy and historical necessity—namely, a truth-maker of a proposition being determinate entails that the proposition is historically necessary. (shrink)

I argue that the semantics of sentences expressing future contingent propositions is best viewed as being based on a clear distinction between a time at which a proposition is true and a time at which a state of affairs that makes it true gets actualized. That a prediction is true here and now means that its truth-maker gets actualized later. This is not to say that if a contingent proposition p concerning the future is true at t, it acquires the (...) truth-value true at t only retrospectively, at a later moment. Nor must this be seen as suggesting that it is a settled, unpreventable fact at t that p is true at t. It just means that the reason for its present truth is something that happens later on: the future happens to evolve in such a way as to make a truth-maker of p obtain. In this case, then, it can be said that at t, p is truth-maker indeterminate, or that it has an indeterminate truth-maker. I develop a formal semantics based on this analysis in the follow-up article ‘A Formal Framework for Future Contingents’. Here, I lay down the conceptual framework and indicate Boethius and Abelard as precursors of the view I wish to defend. (shrink)

The purpose of the paper is to rethink the role of actuality in the branching model of possibilities. We investigate the idea that the model should be enriched with an additional factor—the so-called Thin Red Line—which is supposed to represent the single possible course of events that gets actualized in time. We believe that this idea was often misconceived which prompted some unfortunate reactions. On the one hand, it suggested problematic semantic models of future tense and and on the other, (...) it provoked questionable lines of criticism. We reassess the debate and point to potential pitfalls, focusing on the semantic dimension of the Thin Red Line theory. Our agenda transcends the semantics, however. We conclude that semantic considerations do not threaten the Thin Red Line theory and that the proper debate should be carried in the domain of metaphysics. (shrink)

Is a mathematical theorem proved because provable, or provable because proved? If Brouwer’s intuitionism is accepted, we’re committed, it seems, to the latter, which is highly problematic. Or so I will argue. This and other consequences of Brouwer’s attempt to found mathematics on the intuition of a move of time have heretofore been insufficiently appreciated. Whereas the mathematical anomalies of intuitionism have received enormous attention, too little time, I’ll try to show, has been devoted to some of the temporal anomalies (...) that Brouwer has invited us to introduce into mathematics. (shrink)

In this paper I address issues related to the problem of future contingents and the metaphysical doctrine of fatalism. Two classical responses to the problem of future contingents are the third truth value view and the all-false view. According to the former, future contingents take a third truth value which goes beyond truth and falsity. According to the latter, they are all false. I here illustrate and discuss two ways to respectively argue for those two views. Both ways are similar (...) in spirit and intimately connected with fatalism, in the sense that they engage with the doctrine of fatalism and accept a large part of a standard fatalistic machinery. (shrink)

In this article, we tell a story about incompleteness in modal logic. The story weaves together an article of van Benthem, “Syntactic aspects of modal incompleteness theorems,” and a longstanding open question: whether every normal modal logic can be characterized by a class of completely additive modal algebras, or as we call them, ${\cal V}$-baos. Using a first-order reformulation of the property of complete additivity, we prove that the modal logic that starred in van Benthem’s article resolves the open question (...) in the negative. In addition, for the case of bimodal logic, we show that there is a naturally occurring logic that is incomplete with respect to ${\cal V}$-baos, namely the provability logic $GLB$. We also show that even logics that are unsound with respect to such algebras do not have to be more complex than the classical propositional calculus. On the other hand, we observe that it is undecidable whether a syntactically defined logic is ${\cal V}$-complete. After these results, we generalize the Blok Dichotomy to degrees of ${\cal V}$-incompleteness. In the end, we return to van Benthem’s theme of syntactic aspects of modal incompleteness. (shrink)

This is a sequel article to [10] where a hypersequent calculus for some temporal logics of linear frames includingKt4.3and its extensions for dense and serial flow of time was investigated in detail. A distinctive feature of this approach is that hypersequents are noncommutative, i.e., they are finite lists of sequents in contrast to other hypersequent approaches using sets or multisets. Such a system in [10] was proved to be cut-free HC formalization of respective logics by means of semantical argument. In (...) this article we present an equivalent variant of this calculus for which a constructive syntactical proof of cut elimination is provided. (shrink)

Mereotopology is the discipline obtained from combining topology with the formal study of parts and their relation to wholes, or mereology. This article develops a mereotopological theory of time, illustrating how different temporal topologies can be effectively discriminated on this basis. Specifically, we demonstrate how the three principal types of temporal models—namely, the linear ones, the forking ones, and the circular ones—can be characterized by differently combining two sole mereotopological constraints: one to denote the absence of closed loops, and the (...) other one to denote the absence of branches. (shrink)

The transition semantics presented in Rumberg (J Log Lang Inf 25(1):77–108, 2016a) constitutes a fine-grained framework for modeling the interrelation of modality and time in branching time structures. In that framework, sentences of the transition language L_t are evaluated on transition structures at pairs consisting of a moment and a set of transitions. In this paper, we provide a class of first-order definable Kripke structures that preserves L_t-validity w.r.t. transition structures. As a consequence, for a certain fragment of L_t, validity (...) w.r.t. transition structures turns out to be axiomatizable. The result is then extended to the entire language L_t by means of a quite natural ‘Henkin move’, i.e. by relaxing the notion of validity to bundled structures. (shrink)

The paper considers sentences in which “now” occurs in initial position and shows that the meaning they convey differs from the meaning of sentences that are otherwise identical except for “now” occurring in final position. We argue that the occurrence of “now” in initial position triggers a particular kind of modal reading for the sentence to which the adverb is prefixed. A general notion of modal forcing is proposed to provide a uniform account of this kind of reading. Armed with (...) this account, we offer a solution to two tense-modal puzzles, which have to do with fatalism and the possibility of a changing past. (shrink)

In this work we answer a long standing request for temporal embeddings of deontic STIT logics by introducing the multi-agent STIT logic TDS . The logic is based upon atemporal utilitarian STIT logic. Yet, the logic presented here will be neutral: instead of committing ourselves to utilitarian theories, we prove the logic TDS sound and complete with respect to relational frames not employing any utilitarian function. We demonstrate how these neutral frames can be transformed into utilitarian temporal frames, while preserving (...) validity. Last, we discuss problems that arise from employing binary utility functions in a temporal setting. (shrink)

Those inclined to positions in the philosophy of time that take tense seriously have typically assumed that not all regions of space-time are equal: one special region of space-time corresponds to what is presently happening. When combined with assumptions from modern physics this has the unsettling consequence that the shape of this favored region distinguishes people in certain places or people traveling at certain velocities. In this paper I shall attempt to avoid this result by developing a tensed picture of (...) reality that is nonetheless consistent with ‘hypersurface egalitarianism’—the view that all hypersurfaces are equal. (shrink)

In this research I will focus on a basis for a formal model based on an alternative kind of logic invented by Hans Götzsche: Occurrence Logic (Occ Log), which is not based on truth values and truth functionality. Also, I have taken into account tense logic developed and elaborated by A. N. Prior. In this article I will provide a conceptual and logical foundation for formal Occurrence Logic based on symbolic logic and will illustrate the most important relations between symbolic (...) logic and Occurrence Logic. There will be a special need to focus on arguments based on symbolic occurrence logic. The interrelationships and dependencies between symbolic logic and Occ Log could be conducive to an approach that can express and analyse ‘the occurrences of the world’s descriptions based on various logical principles at different moments’. Symbolic Occ Log checks the occurrence conditioning and the priority of occurrences by employing occurrence values. I shall conclude that the desired approach could gradually support me in providing a truth-functional independent first-order predicate calculus that could work on semantic analysis of different propositions within world descriptions. (shrink)

We introduce an effective translation from proofs in the display calculus to proofs in the labelled calculus in the context of tense logics. We identify the labelled calculus proofs in the image of this translation as those built from labelled sequents whose underlying directed graph possesses certain properties. For the basic normal tense logic Kt, the image is shown to be the set of all proofs in the labelled calculus G3Kt.

Scopo del volume è offrire un’introduzione accessibile e rigorosa ai più recenti sviluppi di una fondamentale branca della filosofia del tempo: la filosofia del futuro. Vengono presentate e discusse alcune delle domande chiave del dibattito contemporaneo, ad esempio: il futuro è già scritto o esistono molti cammini alternativi che il tempo è in grado di imboccare? "Esistere" significa semplicemente essere presenti o ci sono veri e propri oggetti futuri? Siamo davvero liberi di scegliere quali azioni compiere e di modificare il (...) corso degli eventi? Il dibattito intorno alle risposte di volta in volta offerte in filosofia esplora un’intrigante zona d’intersezione tra metafisica, logica ed etica, e interessa discipline diverse, come la fisica, la psicologia e l’economia. Non sorprende dunque che la discussione contemporanea sia oramai tanto intricata da risultare ostica ai non addetti ai lavori. Il volume offre gli strumenti necessari per inquadrare le domande sul futuro nella loro reale complessità concettuale, introducendo tutte le indispensabili nozioni tecniche in un linguaggio chiaro e intuitivo. (shrink)

All’interno del dibattito che anima la filosofia temporale esistono numerose correnti di pensiero su quale posizione si debba adottare riguardo al problema del valore di verità delle proposizioni sul futuro. Nella prima parte dell’articolo verrà tracciato il quadro generale della discussione mediante una ricostruzione storica delle varie argomentazioni – da Aristotele e Diodoro Crono a Prior – e verranno analizzate le posizioni che si sono sviluppate, a partire da queste, nell’età contemporanea. Nella seconda parte invece tenterò di mostrare come la (...) competizione fra la teoria del futuro vero e il sistema ockhamista di Prior non si basi su due differenti concetti di contingenza, ma sulla mancata distinzione, all’interno del sistema ockhamista, di due significati di ‘determinato’ e sulla conseguente confusione che investe il concetto di necessità. Una volta recuperata tale distinzione la teoria ockhamista può essere riformulata e le due diverse posizioni si rivelano essere, semplicemente, teorie sulla determinatezza degli stati futuri. / A large number of schools of thought enliven the philosophical debate on how we can manage the truth-values of propositions about the future. In the first part of this paper I’ll draw an overall view of the discussion, proposing an historical reconstruction of the arguments – from Aristotle and Diodoro Crono to Prior – that will give us the instruments to understand the current state of the debate. After that, in the second part, I’ll argue that the discussion between theory of the true future and Prior’s ockhamist theory is not based on two different concepts of contingency, but instead on the lack of distinction between two different meanings of ‘determined’ inside the ockhamist system. Recovering this distinction is the first step to understand that the real competition between the two systems is not about contingency, but only about the determination of the future. (shrink)

We present a logic of agency called LAE whose language includes propositional constants for actions and expectations. The logic is based on Von Wright’s theory of agency in general and his analysis of instrumentality in particular. An axiomatization of the logic, including an independence of agents axiom, is provided and soundness and completeness are shown with respect to its intended class of frames. The framework of LAE will allow us to formally define a manifold of concepts involved in agency theories, (...) including Von Wright’s four elementary forms of action, the notion of forbearance and notions of instrumentality that make reference to an agent’s expectations. (shrink)

In a recently published paper, Patrick Todd (2016, 'Future contingents are all false! On behalf of a Russellian open future') advocates a novel treatment of future contingents. On his view, all statements concerning the contingent future are false. He motivates his semantic postulates by considerations in philosophy of time and modality, in particular by the claim that there is no actual future. I present a number of highly controversial consequences of Todd’s theory. Inadequacy of his semantics might indirectly serve as (...) an argument against the philosophical view underpinning his proposal. (shrink)

In this paper, we study the introduction of modal past temporal operators in Temporal Equilibrium Logic, an hybrid formalism that mixes linear-time modalities and logic programs interpreted under stable models and their characterisation in terms of Equilibrium Logic. We show that Kamp’s translation can also be used to translate the new extension of TEL with past operators into Quantified Equilibrium Logic. Additionally, we provide a method for removing past operators that consists in replacing past-time subformulas by fresh auxiliary atoms, obtaining (...) an equivalent formula, modulo the original alphabet. (shrink)

Viewing the language of modal logic as a language for describing directed graphs, a natural type of directed graph to study modally is one where the nodes are sets and the edge relation is the subset or superset relation. A well-known example from the literature on intuitionistic logic is the class of Medvedev frames $\langle W,R\rangle$ where $W$ is the set of nonempty subsets of some nonempty finite set $S$, and $xRy$ iff $x\supseteq y$, or more liberally, where $\langle W,R\rangle$ (...) is isomorphic as a directed graph to $\langle \wp(S)\setminus\{\emptyset\},\supseteq\rangle$. Prucnal [32] proved that the modal logic of Medvedev frames is not finitely axiomatizable. Here we continue the study of Medvedev frames with extended modal languages. Our results concern definability. We show that the class of Medvedev frames is definable by a formula in the language of tense logic, i.e., with a converse modality for quantifying over supersets in Medvedev frames, extended with any one of the following standard devices: nominals (for naming nodes), a difference modality (for quantifying over those $y$ such that $x\not= y$), or a complement modality (for quantifying over those $y$ such that $x\not\supseteq y$). It follows that either the logic of Medvedev frames in one of these tense languages is finitely axiomatizable---which would answer the open question of whether Medvedev's [31] "logic of finite problems'' is decidable---or else the minimal logics in these languages extended with our defining formulas are the beginnings of infinite sequences of frame-incomplete logics. (shrink)

(...) . (shrink)

Todd (2016) proposes an analysis of future-directed sentences, in particular sentences of the form 'will(φ)', that is based on the classic Russellian analysis of definite descriptions. Todd's analysis is supposed to vindicate the claim that the future is metaphysically open while retaining a simple Ockhamist semantics of future contingents and the principles of classical logic, i.e. bivalence and the law of excluded middle. Consequently, an open futurist can straightforwardly retain classical logic without appeal to supervaluations, determinacy operators, or any further (...) controversial semantical or metaphysical complication. In this paper, we will show that this quasi-Russellian analysis of 'will' both lacks linguistic motivation and faces a variety of significant problems. In particular, we show that the standard arguments for Russell's treatment of definite descriptions fail to apply to statements of the form 'will(φ)'. (shrink)

The so-called theory of karma is one of the distinguishing aspects of Hinduism and other non-Hindu south-Asian traditions. At the same time that the theory can be seen as closely connected with the freedom of will and action that we humans supposedly have, it has many times been said to be determinist and fatalist. The purpose of this paper is to analyze in some deepness the relations that are between the theory of karma on one side and determinism, fatalism and (...) free-will on the other side. In order to do that, I shall use what has been described as the best formal approach we have to indeterminism: branching time theory. More specifically, I shall introduce a branching time semantic framework in which, among other things, statements such as “state of affairs e is a karmic effect of agent a”, “a wills it to be the case that e” and “e is inevitable” could be properly represented. (shrink)

The problem of future contingents is regarded as an important philosophical problem in connection with determinism and it should be treated by tense logic. Prior’s early work focused on the problem, and later Prior studied branching-time tense logic which was invented by Kripke. However, Prior’s idea to use three-valued logic for the problem seems to be still alive. In this paper, we consider partial and paraconsistent approaches to the problem of future contingents. These approaches theoretically meet Aristotle’s interpretation of future (...) contingents. (shrink)