Many philosophical discussions hinge on the concept of knowability. For example, there is a blooming literature on the so-called paradox of knowability. How to understand this notion, however? In this paper, we examine several approaches to the notion: the naive approach to take knowability as the possibility to know, the counterfactual approach endorsed by Edgington (1985) and Schlöder (2019) , approaches based on the notion of a capacity or ability to know (Fara 2010, Humphreys 2011), and finally, approaches that make (...) use of the resources of dynamic epistemic logic (van Benthem 2004, Holliday 2017). (shrink)

Tarski's analysis of the concept of truth gives rise to a hierarchy of languages. Does this fragment the concept all the way to philosophical unacceptability? I argue it doesn't, drawing on a modification of Kaplan's theory of indexicals.

In this paper, I claim that two ways of defining validity for modal languages (“real-world” and “general” validity), corresponding to distinction between a correct and an incorrect way of defining modal valid- ity, correspond instead to two substantive ways of conceiving modal truth. At the same time, I claim that the major logical manifestation of the real- world/general validity distinction in modal propositional languages with the actuality operator should not be taken seriously, but simply as a by-product of the way (...) in which the semantics of such an operator is usually given. (shrink)

Aristotelian Actualism is the conjunction of the theses that absolutely everything is actual, that individuals are neither reducible to nor dependent on independently identified properties, and that some individuals are genuine contingent existents. Robert Adams and Gregory Fitch, two prominent proponents of Aristotelian Actualism, have argued that this view has a consequence that any modal logic stronger than M, and so any modal logic in which symmetry and reflexivity are frame conditions, is inadequate. We argue that this is incorrect.

In this note we show that the classical modal technology of Sahlqvist formulas gives quick proofs of the completeness theorems in [8] (D. Gregory, Completeness and decidability results for some propositional modal logics containing "actually" operators, Journal of Philosophical Logic 30(1): 57-78, 2001) and vastly generalizes them. Moreover, as a corollary, interpolation theorems for the logics considered in [8] are obtained. We then compare Gregory's modal language enriched with an "actually" operator with the work of Arthur Prior now known under (...) the name of hybrid logic. This analysis relates the "actually" axioms to standard hybrid axioms, yields the decidability results in [8], and provides a number of complexity results. Finally, we use a bisimulation argument to show that the hybrid language is strictly more expressive than Gregory's language. (shrink)

Ted A. Warfield has recently employed modal logic to argue that compatibilism in the free-will/determinism debate entails the rejection of intuitively valid inferences. I show that Warfield's argument fails. A parallel argument leads to the false conclusion that the mere possibility of determinism, together with the necessary existence of any contingent propositions, entails the rejection of intuitively valid inferences. The error in both arguments involves a crucial equivocation, which can be revealed by replacing modal operators with explicit quantifiers over possible (...) worlds. I conclude that the modal-logical apparatus used by Warfield obscures rather than clarifies, and distracts from the real philosophical issues involved in the metaphysical debate. These issues cannot be settled by logic alone. (shrink)

The paper is an investigation into the concept of actuality from the standpoint of the philosophy of language. It is argued that expressions such as 'actually' and 'in fact' are not indexicals like 'here' and 'now'; when e.g. 'Snow is actually white' is uttered in a world, what proposition is conveyed does not depend on the world. Nor are such expressions ambiguous. The paper makes a suggestion about the role that 'actually' and its cognates do play. It is also argued (...) that the sentence ⌜Actually S ⌝ expresses a necessary truth only if S itself expresses one. In order to capture the necessitation of the proposition expressed in ⌜Actually S ⌝, it is not sufficient to prefix the word 'necessarily'. (shrink)

We show that the actuality operator A is redundant in any propositional modal logic characterized by a class of Kripke models (respectively, neighborhood models). Specifically, we prove that for every formula ${\phi}$ in the propositional modal language with A, there is a formula ${\psi}$ not containing A such that ${\phi}$ and ${\psi}$ are materially equivalent at the actual world in every Kripke model (respectively, neighborhood model). Inspection of the proofs leads to corresponding proof-theoretic results concerning the eliminability of the actuality (...) operator in the actuality extension of any normal propositional modal logic and of any “classical” modal logic. As an application, we provide an alternative proof of a result of Williamson’s to the effect that the compound operator A□ behaves, in any normal logic between T and S5, like the simple necessity operator □ in S5. (shrink)

Our concern here is with the extent to which the expressive equivalence of Wehmeier’s Subjunctive Modal Language and the Actuality Modal Language is sensitive to the choice of background modal logic. In particular we will show that, when we are enriching quantified modal logics weaker than S5, AML is strictly expressively stronger than SML, this result following from general considerations regarding the relationship between operators and predicate markers. This would seem to complicate arguments given in favour of SML which rely (...) upon its being expressively equivalent to AML. (shrink)

Ratio, Volume 35, Issue 2, Page 104-111, June 2022.

We investigate and compare two major approaches to enhancing the expressive capacities of modal languages, namely the addition of subjunctive markers on the one hand, and the addition of scope-bearing actuality operators, on the other. It turns out that the subjunctive marker approach is not only every bit as versatile as the actuality operator approach, but that it in fact outperforms its rival in the context of cross-world predication.