C. Lewy; VI—Entailment and Propositional Identity, Proceedings of the Aristotelian Society, Volume 64, Issue 1, 1 June 1964, Pages 107–122, https://doi.org/10.1.

In two early papers, Max Cresswell constructed two formal logics of propositional identity, pcr and fcr, which he observed to be respectively deductively equivalent to modal logics s4 and s5. Cresswell argued informally that these equivalences respectively “give . . . evidence” for the correctness of s4 and s5 as logics of broadly logical necessity. In this paper, I describe weaker propositional identity logics than pcr that accommodate core intuitions about identity and I argue that (...) Cresswell’s informal arguments do not firmly and without epistemic circularity justify accepting s4 or s5. I also describe how to formulate standard modal logics (k, s2, and their extensions) with strict equivalence as the only modal primitive. (shrink)

I show that standard grounding conditions contradict standard conditions for the identities of propositions.

By following a recent result of [Wilhelm, 2021], it can easily be shown that standard conditions for immediate partial grounding and relevant identity conditions for propositions are inconsistent with one another. This is an unfortunate situation for all grounding enthusiasts; however, by adopting the approach presented by Poggiolesi [2016a,b], which displays a more-fined grained use of negations, it can also be shown that consistency can be restored back.

We give a semantical account of propositional identity which is stronger than mutual entailment. That is, according to our account: (1) if A = B is true in a model, so are A 'validates' B and B 'validates' A. (2) There exist models m such that A 'validates' B and B 'validates' A are true in m but A = B is not true in m. According to our account the following rule is sound: (3) from (.. A..) (...) = (.. B..) infer A = B. The paper is a response to a paper by James Freeman to an earlier paper by us. (shrink)

Let A, B, C stand for sentences expressing propositions; let A be a component of C; let C A/B be just like C except for replacing some occurrence of A in C by an occurrence of B; let = be a binary connective for propositional identity read as ‘the proposition that __ is the very same proposition as …’. Then authors defend adding ‘from C = C A/B infer A = B’ to Prior’s rules for propositional (...) class='Hi'>identity, appearing in OBJECTS OF THOUGHT. (shrink)

Propositional identity is not expressed by a predicate. So its logic is not given by the ordinary first order axioms for identity. What are the logical axioms governing this concept, then? Some axioms in addition to those proposed by Arthur Prior are proposed.

The paper is an extended version of a talk given to the XXXth Conference on the History of Logic devoted to the work of Professor Roman Suszko . Its aim is to present Sentential Calculus with Identity in comparison with other formalizations of propositional identity.

Anderson and Belnap devise a model theory for entailment on which propositional identity equals proposional coentailment. This feature can be reasonably questioned. The authors devise two extensions of Anderson and Belnap’s model theory. Both systems preserve Anderson and Belnap’s results for entailment, but distinguish coentailment from identity.

We study natural deduction systems for a fragment of intuitionistic logic with propositional identity from the point of view of proof-theoretic semantics. We argue that the identity connective is a natural operator to be treated under the elimination rules as basic approach.

Many systems of quantified modal logic cannot be characterised by Kripke's well-known possible worlds semantic analysis. This book shows how they can be characterised by a more general 'admissible semantics', using models in which there is a restriction on which sets of worlds count as propositions. This requires a new interpretation of quantifiers that takes into account the admissibility of propositions. The author sheds new light on the celebrated Barcan Formula, whose role becomes that of legitimising the Kripkean interpretation of (...) quantification. The theory is worked out for systems with quantifiers ranging over actual objects, and over all possibilia, and for logics with existence and identity predicates and definite descriptions. The final chapter develops a new admissible 'cover semantics' for propositional and quantified relevant logic, adapting ideas from the Kripke-Joyal semantics for intuitionistic logic in topos theory. This book is for mathematical or philosophical logicians, computer scientists and linguists. (shrink)

In this paper we discuss the distinction between sentence and proposition from the perspective of identity. After criticizing Quine, we discuss how objects of logical languages are constructed, explaining what is Kleene’s congruence—used by Bourbaki with his square—and Paul Halmos’s view about the difference between formulas and objects of the factor structure, the corresponding boolean algebra, in case of classical logic. Finally we present Patrick Suppes’s congruence approach to the notion of proposition, according to which a whole hierarchy of (...) congruences leads to different kinds of objects. (shrink)

Previously unpublished passages from the Cairns Nachlass are assembled and commented on to present the identity theory in contrast with the traditional coherence and correspondence theories, and then seven more detailed analyses of related aspects are also edited.To say that a syntactical object is true or is a fact, is to say that the act of intending it as having a perhaps indistinct structure and a perhaps obscure material content may unite in a positive synthesis of identification with an (...) act wherein “the same” syntactical object is distinctly and clearly evident as having “the same” structure and content. The fulfilling act is eo ipso a grasping of the still grasped syntactical object as having been produced by a syntactical activity founded in original explication of the subject-matter. The realization of such a synthesis is a verification of the truth of the syntactical object, a verification of the “existence” of the fact.Se reúnen y comentan pasajes inéditos del Nachlass de Cairns para presentar la teoría de la identidad en contraste con las tradicionales de la coherencia y la correspondencia, también se editan luego siete análisis más detallados de aspectos relacionados.Decir que un objeto sintáctico es cierto o es un hecho, es decir que el acto de mentarlo como teniendo una estructura tal vez confusa y un contenido material tal vez os-curo, puede unir en una síntesis positiva de identificación con un acto en el que "el mismo" objeto sintáctico es clara y evidentemente teniendo "la misma" estructura y contenido. El acto de cumplimiento es eo ipso un captación del objeto sintáctico todavía captado como habiendo sido producido por una actividad sintáctica fundada en explicación original de la materia. La realización de tal síntesis es una verificación de la verdad del objeto sintáctico, una verificación de la "existencia" del hecho. (shrink)

There are logics where necessity is defined by means of a given identity connective: \ is a tautology). On the other hand, in many standard modal logics the concept of propositional identity \ can be defined by strict equivalence \}\). All these approaches to modality involve a principle that we call the Collapse Axiom : “There is only one necessary proposition.” In this paper, we consider a notion of PI which relies on the identity axioms of (...) Suszko’s non-Fregean logic SCI. Then S3 proves to be the smallest Lewis modal system where PI can be defined as SE. We extend S3 to a non-Fregean logic with propositional quantifiers such that necessity and PI are integrated as non-interdefinable concepts. CA is not valid and PI refines SE. Models are expansions of SCI-models. We show that SCI-models are Boolean prealgebras, and vice-versa. This associates non-Fregean logic with research on Hyperintensional Semantics. PI equals SE iff models are Boolean algebras and CA holds. A representation result establishes a connection to Fine’s approach to propositional quantifiers and shows that our theories are conservative extensions of S3–S5, respectively. If we exclude the Barcan formula and a related axiom, then the resulting systems are still complete w.r.t. a simpler denotational semantics. (shrink)

We construct a a system PLRI which is the classical propositional logic supplied with a ternary construction , interpreted as the intensional identity of statements and in the context . PLRI is a refinement of Roman Suszko’s sentential calculus with identity (SCI) whose identity connective is a binary one. We provide a Hilbert-style axiomatization of this logic and prove its soundness and completeness with respect to some algebraic models. We also show that PLRI can be used (...) to give a partial solution to the paradox of analysis. (shrink)

This is a paper in which I argue that problems of transworld identity and the truth in-truth at distinction are motivated by unhelpful pictures we have in mind while doing metaphysics.

A comparison is given between two conditions used to define logical constants: Belnap's uniqueness and Hacking's deducibility of identicals. It is shown that, in spite of some surface similarities, there is a deep difference between them. On the one hand, deducibility of identicals turns out to be a weaker and less demanding condition than uniqueness. On the other hand, deducibility of identicals is shown to be more faithful to the inferentialist perspective, permitting definition of genuinely proof-theoretical concepts. This kind of (...) analysis is driven by exploiting the Curry–Howard correspondence. In particular, deducibility of identicals is shown to correspond to the computational property of eta expansion, which is essential in the characterization of propositional identity. (shrink)

The pressure to individuate propositions more finely than intensionally—that is, hyper-intensionally—has two distinct sources. One source is the philosophy of mind: one can believe a proposition without believing an intensionally equivalent proposition. The second source is metaphysics: there are intensionally equivalent propositions, such that one proposition is true in virtue of the other but not vice versa. I focus on what our theory of propositions should look like when it's guided by metaphysical concerns about what is true in virtue of (...) what. In this paper I articulate and defend a metaphysical theory of the individuation of propositions, according to which two propositions are identical just in case they occupy the same nodes in a network of invirtuation relations. Invirtuation is here taken to be a primitive relation of metaphysical explanation exemplified by propositions that, in conjunction with truth, defines the notion of true in virtue of. After formulating the theory, I compare it with a view.. (shrink)

This paper consists of an investigation of three debates concerning propositional identity: the tension between structured propositions and higher-order logic, the principle Only Logical Circles, and Kaplan’s Paradox. The literature at large has mistaken the consequences of each of these debates. Structuralists are not committed to the claim that identical properties have different extensions; rather, they are committed to existence monism. Only Logical Circles does not preclude the identification of green in terms of grue; some further (and, as (...) of yet, undisclosed) principle is required for that result. And Kaplan’s Paradox does not count against the possible-worlds conception of propositions; it applies to every account of propositions whatsoever. (shrink)

Bolzano's Sätze an sich and Frege's Gedanken are obviously close relatives. The paper underlines both similarities and dissimilarities between the psychological and semantical roles assigned to structured truth-evaluable contents in Bolzano's and Frege's theories. In particular, their different accounts of propositional identity are compared, and it is argued that Dummett's recent criticism of Frege's account is grist to Bolzano's mill.

Propositions are the result of hypostatization in accordance with the principle of the identification of indiscernibles wherever differences among inscribed or uttered statemental units are systematically ignored. Criteria for identity of propositions are, thus, to be found in each context of discourse about statemental units where qualitatively different units are treated as interchangeable. Ayer's notion of proposition as opposed to statement, Goodman's notion of replication, and the notion of constructional definition or reduction are discussed in the light of this (...) thesis. The so-called "problem of identifying propositions" is shown to be a bogus problem because the propositions simpliciter to be identified are incoherently conceived, though in the course of discussion the prospect appears that many different and limitedly applicable sets of criteria for identification of propositions relative to different discourses can be given. (shrink)

This paper develops a theory of propositional identity which distinguishes necessarily equivalent propositions that differ in subject-matter. Rather than forming a Boolean lattice as in extensional and intensional semantic theories, the space of propositions forms a non-interlaced bilattice. After motivating a departure from tradition by way of a number of plausible principles for subject-matter, I will provide a Finean state semantics for a novel theory of propositions, presenting arguments against the convexity and nonvacuity constraints which Fine (2016, 2017a,b) (...) introduces. I will then move to compare the resulting logic of propositional identity (PI) with Correia’s (2016) logic of generalised identity (GI), as well as the first degree fragment of Angell’s (1989) logic of analytic containment (AC). The paper concludes by extending PI to include axioms and rules for a subject-matter operator, providing a much broader theory of subject-matter than the principles with which I will begin. (shrink)

We construct a Hilbert style system RPL for the notion of plausibility measure introduced by Halpern J, and we prove the soundness and completeness with respect to a neighborhood style semantics. Using the language of RPL, we demonstrate that it can define well-studied notions of necessity, conditionals and propositional identity.

Soames's cognitive propositions are strings of acts to be performed by an agent, such as predicating a property of an individual. King takes these structured propositions to task for proliferating too easily. King's objection is based on an example that purports to show that three of Soames's propositions are really just one proposition. I translate the informally stated propositions King attributes to Soames into the intensional λ-calculus. It turns out that they are all β-equivalent to the proposition King claims Soames's (...) three propositions are identical to. I argue on philosophical grounds against identifying β-equivalent propositions. The reason is that β-conversion obliterates too many of the procedural distinctions that are central to an act-based theory such as Soames's and which are worth preserving. In fact, β-expansion allows the addition of a fifth proposition that highlights additional procedural distinctions and propositional structure. The welcome conclusion is that we have five procedurally distinct, if equivalent, propositions. (shrink)

In Frege’s Puzzle, Nathan Salmon argues that his theory of singular propositions enables him to refute Saul Kripke’s claim that some identity statements are necessary and yet a posteriori. In this paper, through a critical examination of Salmon’s rejoinders to my earlier objections to his argument, I show what implications the theory of singular propositions has for the notion of apriority. I argue that Salmon’s handling of the ‘trivialization problem,’ which presents serious difficulties for his ‘absolute’ account of apriority, (...) leaves a great deal to be desired. I suggest, in conclusion, that the theorist of singular propositions should hold a relative view of apriority. (shrink)

Our purpose is to formulate a complete logic of propositions that takes into account the fact that propositions are both senses provided with truth values and contents of conceptual thoughts. In our formalization, propositions are more complex entities than simple functions from possible worlds into truth values. They have a structure of constituents (a content) in addition to truth conditions. The formalization is adequate for the purposes of the logic of speech acts. It imposes a stronger criterion of propositional (...) identity than strict equivalence. Two propositions P and Q are identical if and only if, for any illocutionary force F, it is not possible to perform with success a speech act of the form F(P) without also performing with success a speech act of the form F(Q). Unlike hyperintensional logic, our logic of propositions is compatible with the classical Boolean laws of propositional identity such as the symmetry and the associativity of conjunction and the reduction of double negation. (shrink)

ABSTRACT In ‘Properties, Propositions, and Conditionals’ Field [2021] advances further on our understanding of the logic and meaning of naive theories – theories that maintain, in the face of paradox, basic assumptions about properties and propositions. His work follows in a tradition going back over 40 years now, of using Kripke fixed-point model constructions to show how naive schemas can be (Post) consistent, as long as one embeds in a non-classical logic. A main issue in all this research is the (...) question of finding a suitable conditional for the naive schemas, an implication connective that is well-behaved enough to be useful but weak enough to maintain coherence when there are paradoxes in the surrounding aether. Field takes several cues from the exemplary work of Ross Brady. Brady's work is predominantly concerned with models for naive theories in relevant logic. Field's considered view is that ‘relevant conditionals are just the wrong tool for naive theories’ [ibid.: 140]. In this note, I reply that a relevant conditional is an indispensable tool for at least one very important job: giving identity conditions for properties. (shrink)

This paper examines the potential for abstracting propositions – an as yet untested way of defending the realist thesis that propositions as abstract entities exist. I motivate why we should want to abstract propositions and make clear, by basing an account on the neo-Fregean programme in arithmetic, what ontological and epistemological advantages a realist can gain from this. I then raise a series of problems for the abstraction that ultimately have serious repercussions for realism about propositions in general. I first (...) identify problems about the number of entities able to be abstracted using these techniques. I then focus on how issues of language relativity result in problems akin to the Caesar problem in arithmetic by exposing circularity and modal concern over the status of the criterion of identity for propositions. (shrink)

This manuscript focuses on a problem for Millian Russellianism raised by Fine : “[Assuming] that we are in possession of the information that a Fs and the information that a Gs, it appears that we are sometimes justified in putting this information ‘together’ and inferring that a both Fs and Gs. But how?” It will be my goal to determine a Millian-Russellian solution to this problem. I will first examine Nathan Salmon’s Millian-Russellian solution, which appeals to a non-semantic and subjective (...) notion of coordination defined in terms of guises. I will object that in order to convincingly solve a specific version of Fine’s problem, identity conditions for guises must be provided. On the other hand, the most plausible way to individuate guises is by means of the equivalence classes of coordination itself. But, if so, the guise-based strategy to solve Fine’s problem risks being circular; in addition, there are serious doubts that coordination is transitive. An alternative Millian-Russellian solution to Fine’s problem will then be explored, which gives up guises and employs, instead, a non-semantic and subjective relation of coordination not defined in terms of guises, along with occurrences of Russellian propositions of a special sort, for which identity conditions will be provided and via which token attitude states intuitively more fine-grained than guises will be individuated. (shrink)

Having briefly sketched the aims of our paper, namely, to logically analyse the ascription of propositional attitudes to somebody else in terms, not of Fregean senses or of intensions-with-s, but of the intentional object of the person spoken about, say, the believer or intender (Section 1), we try to introduce the concept of an intentional object as simply as possible, to wit, as coming into view whenever two (or more) subjective belief-worlds strikingly diverge (Section 2). Then, we assess the (...) pros and cons of Frege’s view that the indirect reference of an expression is nothing but its customary sense (Sections 3–4), and call the reader’s attention to the fact that in belief ascriptions de re we take it for granted that the believer’s intentional object is at the same time a ‘citizen’ of the belief ascriber’s subjective world (or, for that matter, the real word), and that the idea of such a ‘dual citizenship’ is even more obviously presupposed in the cases of true belief and propositional knowledge (Section 5). Then, we try to argue that it is more fertile to take the belief ascriber’s intentional object to be, not the whole state of affairs the believer has in mind and thinks to exist, but the latter’s intentional object as such, that is, as being his intentional object (Section 6). Finally, we discuss the intricate and mostly neglected question of whether an intentional object’s inhabiting two or more subjective belief-worlds should be considered to be sort of a ‘transmundane identity’ in the numerical sense or rather in some deviant sense of the term, which can be specified as a momentous subcase of a ‘categorial difference’ (Section 7). (shrink)

Our linguistic and inferential practices are said to implicate a kind of abstract object playing various roles traditionally attributed to propositions, and our predictive and explanatory success with this ‘‘proposition-talk’’ is held to underwrite a realistic interpretation of it. However, these very same practices pull us in different directions regarding the nature of propositions, frustrating the development of an adequate unified theory of them. I explain how one could retain proposition-talk, and the advantages of interpreting it as being purportedly about (...) propositions, even if problems about the identity conditions for propositions motivated a Quinean rejection of them. The non-error-theoretic solution is to understand proposition-talk in terms of semantic pretense. On this approach, talking as if there were propositions lets us put readily available logical and linguistic devices to new expressive purposes, providing a way to make indirectly certain complicated, genuinely true assertions we cannot make directly. Proposition-talk thus extends the expressive capacity of a language in a logico-syntactically conservative way. (shrink)

In his Grundgesetze, §32, Frege launched the idea that the meaning of a sentence is given by its truth condition, or, in his particular version, the condition under which it will be a name of the True. This, indeed, was only one of the many roles in which truth has to serve within the Fregean system. In particular, truth is an absolute notion in the sense that bivalence holds: every Gedanke is either true or false, in complete independence of any (...) conative activity, whether by God or man. Thus various epistemological notions, such as the correctness of an assertion made, or judgement passed, are reducible to this absolute notion of truth: an assertion made through the utterance of a declarative sentence is correct when the proposition expressed by the sentence in question is true. Given this absolute status of truth it is not surprising that Frege is of the opinion that truth is a sui generis notion which has to be left unanalyzed and, indeed, which is indefinable. (shrink)