Lindström’s Theorem characterizes first order logic as the maximal logic satisfying the Compactness Theorem and the Downward Löwenheim-Skolem Theorem. If we do not assume that logics are closed under negation, there is an obvious extension of first order logic with the two model theoretic properties mentioned, namely existential second order logic. We show that existential second order logic has a whole family of proper extensions satisfying the Compactness Theorem and the Downward Löwenheim-Skolem Theorem. Furthermore, we (...) show that in the context of negation-less logics, _positive logics_, as we call them, there is no strongest extension of first order logic with the Compactness Theorem and the Downward Löwenheim-Skolem Theorem. (shrink)

We consider a simple modal logic whose nonmodal part has conjunction and disjunction as connectives and whose modalities come in adjoint pairs, but are not in general closure operators. Despite absence of negation and implication, and of axioms corresponding to the characteristic axioms of _T_, _S4_, and _S5_, such logics are useful, as shown in previous work by Baltag, Coecke, and the first author, for encoding and reasoning about information and misinformation in multiagent systems. For the propositional-only fragment of (...) such a dynamic epistemic logic, we present an algebraic semantics, using lattices with agent-indexed families of adjoint pairs of operators, and a cut-free sequent calculus. The calculus exploits operators on sequents, in the style of “nested” or “tree-sequent” calculi; cut-admissibility is shown by constructive syntactic methods. The applicability of the logic is illustrated by reasoning about the muddy children puzzle, for which the calculus is augmented with extra rules to express the facts of the muddy children scenario. (shrink)

Positive logics are $\{ \wedge, \vee, \to \}$-fragments of intermediate logics. It is clear that the positive fragment of $Int$ is not structurally complete. We give a description of all hereditarily structurally complete positive logics, while the question whether there is a structurally complete positive logic which is not hereditarily structurally complete, remains open.

A formal language is positional if it involves a positional connecitve, i.e. a connective of realization to relate formulas to points of a kind, like points of realization or points of relativization. The connective in focus in this paper is the connective “R”, first introduced by Jerzy Łoś. Formulas [Rαφ] involve a singular name α and a formula φ to the effect that φ is satisfied relative to the position designated by α. In weak positional calculi no nested occurences of (...) the connective “R” are allowed. The distribution problem in weak positional logics is actually the problem of distributivity of the connective “R” over classical connectives, viz. the problem of relation between the occurences of classical connectives inside and outside the scope of the positional connective “R”. (shrink)

Proof-theoretic methods are developed for subsystems of Johansson’s logic obtained by extending the positive fragment of intuitionistic logic with weak negations. These methods are exploited to establish properties of the logical systems. In particular, cut-free complete sequent calculi are introduced and used to provide a proof of the fact that the systems satisfy the Craig interpolation property. Alternative versions of the calculi are later obtained by means of an appropriate loop-checking history mechanism. Termination of the new calculi (...) is proved, and used to conclude that the considered logical systems are PSPACE-complete. (shrink)

In this paper we extend of the notion of algebraically closed given in the case of groups and skew fields to an arbitrary h-inductive theory. The main subject of this paper is the study of the notion of positive algebraic closedness and its relationship with the notion of positive closedness and the amalgamation property.

We introduce prime products as a generalization of ultraproducts for positive logic. Prime products are shown to satisfy a version of Łoś’s Theorem restricted to positive formulas, as well as the following variant of the Keisler Isomorphism Theorem: under the generalized continuum hypothesis, two models have the same positive theory if and only if they have isomorphic prime powers of ultrapowers.

The goal of the article is twofold. The first one is to provide logics based on positional semantics which will be suitable for the analysis of epistemic modalities such as ‘agent... knows/beliefs that...’. The second one is to define tableau systemsfor such logics. Firstly, we present the minimal positional logic MR. Then, we change the notion of formulas and semantics in order to consider iterations of the operator of realization and “free” classical formulas. After that, we move on to (...) weaker logics in order to avoid the well known problem of logical omniscience. At the same time, we keep the positional counterparts of modal axioms, and. For all of the considered logics we present sound and complete tableau systems. (shrink)

The paper studies admissibility of multiple-conclusion rules in positive logics. Using modification of a method employed by M. Wajsberg in the proof of the separation theorem, it is shown that the problem of admissibility of multiple-conclusion rules in the positive logics is equivalent to the problem of admissibility in intermediate logics defined by positive additional axioms. Moreover, a multiple-conclusion rule \ follows from a set of multiple-conclusion rules \ over a positive logic \ if and (...) only if \ follows from \ over \. (shrink)

We construct a 2-equivalence \(\mathfrak {CohTheory}^{op }\simeq \mathfrak {TypeSpaceFunc}\). Here \(\mathfrak {CohTheory}\) is the 2-category of positive theories and \(\mathfrak {TypeSpaceFunc}\) is the 2-category of type space functors. We give a precise definition of interpretations for positive logic, which will be the 1-cells in \(\mathfrak {CohTheory}\). The 2-cells are definable homomorphisms. The 2-equivalence restricts to a duality of categories, making precise the philosophy that a theory is ‘the same’ as the collection of its type spaces (i.e. its (...) type space functor). In characterising those functors that arise as type space functors, we find that they are specific instances of (coherent) hyperdoctrines. This connects two different schools of thought on the logical structure of a theory. The key ingredient, the Deligne completeness theorem, arises from topos theory, where positive theories have been studied under the name of coherent theories. (shrink)

Our question is: can we embed minimal negation in implicative logics weaker than I→? Previous results show how to define minimal negation in the positive fragment of the logic of relevance R and in contractionless intuitionistic logic. Is it possible to endow weaker positive logics with minimal negation? This paper prooves that minimal negation can be embedded in even such a weak system as Anderson and Belnap’s minimal positive logic.

A sufficient condition for an extension of positive logic with strong negation to be characterized by a class of finite trees is given.

Entendemos el concepto de “negación mínima” en el sentido clásico definido por Johansson. El propósito de este artículo es definir la lógica positiva mínima Bp+, y probar que la negación mínima puede introducirse en ella. Además, comentaremos algunas de las múltiples extensiones negativas de Bp+.“Minimal negation” is classically understood in a Johansson sense. The aim of this paper is to define the minimal positive logic Bp+ and prove that a minimal negation can be inroduced in it. In addition, (...) some of the many possible negation extensions of Bp+ are commented. (shrink)

Entendemos el concepto de “negación mínima” en el sentido clásico definido por Johansson. El propósito de este artículo es definir la lógica positiva mínima Bp+, y probar que la negación mínima puede introducirse en ella. Además, comentaremos algunas de las múltiples extensiones negativas de Bp+.“Minimal negation” is classically understood in a Johansson sense. The aim of this paper is to define the minimal positive logic Bp+ and prove that a minimal negation can be inroduced in it. In addition, (...) some of the many possible negation extensions of Bp+ are commented. (shrink)

Positive monotone modal logic is the negation- and implication-free fragment of monotone modal logic, i.e., the fragment with connectives and. We axiomatise positive monotone modal logic, give monotone neighbourhood semantics based on posets, and prove soundness and completeness. The latter follows from the main result of this paper: a duality between so-called \-spaces and the algebraic semantics of positive monotone modal logic. The main technical tool is the use of coalgebra.

We give a set of postulates for the minimal normal modal logicK + without negation or any kind of implication. The connectives are simply , , , . The postulates (and theorems) are all deducibility statements . The only postulates that might not be obvious are.

CHAPTER 1 From Bentham to Kanger I. Introduction In the analytical tradition established by Jeremy Bentham and John Austin, and continued in the twentieth ...

In this paper is constructed an analogue of the square of opposition for propositions about relations between two non-empty sets. Unlike the classical square of opposition, the proposed scheme uses all logically possible syllogistic constants, formulated in V.I. Markin’s universal language for traditional positive syllogistic theories. This scheme can be called “Logical lantern”. The basic constants of this language are representing the five basic relations between two non-empty sets: equity, strict inclusion, reversed strict inclusion, intersection and exclusion (considered are (...) only the relations between sets, but not the relations of the sets to the universe). The other relations between sets are combinations (disjunctions) of the basic ones. There are 32 constants and 32 respective propositions, and the proposed diagram expresses and/or allows to deduce the logical relations among those propositions. The constructed scheme, making it possible to visually see the logical relations among propositions about relations between two non-empty sets, allows us to suggest considering logical relations not discussed previously: many-place Aristotelian-like logical relations among propositions: exhaustive _n_-place contrariety and exhaustive _n_-place subcontrariety (_n_ is a natural number, \(n>2\) ). (shrink)

We deal with the fragment of modal logic consisting of implications of formulas built up from the variables and the constant ‘true’ by conjunction and diamonds only. The weaker language allows one to interpret the diamonds as the uniform reflection schemata in arithmetic, possibly of unrestricted logical complexity. We formulate an arithmetically complete calculus with modalities labeled by natural numbers and ω, where ω corresponds to the full uniform reflection schema, whereas n<ω corresponds to its restriction to arithmetical Πn+1-formulas. (...) This calculus is shown to be complete w.r.t. a suitable class of finite Kripke models and to be decidable in polynomial time. (shrink)

We prove that compactness is equivalent to the amalgamation property, provided the occurrence number of the logic is smaller than the first uncountable measurable cardinal. We also relate compactness to the existence of certain regular ultrafilters related to the logic and develop a general theory of compactness and its consequences. We also prove some combinatorial results of independent interest.

Performing an inference involves irreducibly dynamic cognitive procedures. The article proposes that a non-associative information frame, corresponding to a residuated pogroupoid, underpins the information structure involved. The argument proceeds by expounding the informational turn in logic, before outlining the cognitive actions at work in deductive inference. The structural rules of Weakening, Contraction, Commutation, and Association are rejected on the grounds that they cause us to lose track of the information flow in inferential procedures. By taking the operation of information (...) application as the primary operation, the fusion connective is retained, with commutative failure generating a double implication. The other connectives are rejected. (shrink)

Acts of criticism characteristically display a negative and a positive dimension. I undertake a qualified defense of the thesis that both dimensions are essential, at least in the case of logical criticism – criticism that relies either implicitly or explicitly on the resources of logic. Such criticism presupposes at least a minimal grasp on what is involved in ‘getting it right’ in the domain that is subjected to critique. In making the case I distinguish between positive and (...) negative logic. Traditional logic is positive insofar as it takes as primitive a positive notion, typically truth. I consider to what extent logic might be reconstructed on an exclusively negative basis – as a tool for avoiding falsity and fallacy. Negative logic faces serious obstacles which suggest a prima facie case that logical criticism is essentially, not just accidentally, positive. (shrink)

The positive fragment of the local modal consequence relation defined by the class of all Kripke frames is studied in the context ofAlgebraic Logic. It is shown that this fragment is non-protoalgebraic and that its class of canonically associated algebras according to the criteria set up in [7] is the class of positive modal algebras. Moreover its full models are characterized as the models of the Gentzen calculus introduced in [3].

We prove that algebras of binary relations whose similarity type includes intersection, union, and one of the residuals of relation composition form a nonfinitely axiomatizable quasivariety and that the equational theory is not finitely based. We apply this result to the problem of the completeness of the positive fragment of relevance logic with respect to binary relations.

1960년대에 집중적으로 제기된 논리경험주의에 대한 대다수의 철학적 공격은 이른바 논리경험주의의 ‘수용된 견해’를 향한 것이었고, 이후 과학철학자들이 공공연히 ‘논리경험주의는 죽었다’라는 표현을 쓸 정도로까지 논리경험주의 과학철학의 위상은 낮아졌다. 문제는 이와 같은 논리경험주의의 ‘수용된 견해’가 대부분 비엔나 학파를 대표하는 카르납의 철학적 관점을 반영하고 있다는 데 있다. 최근의 논리경험주의에 대한 역사철학적 탐구가 보여주듯, 논리경험주의 내에 다양성이 존재했고 특히 카르납으로 대표되는 비엔나 학파와 라이헨바흐로 대표되는 베를린 학파 사이에는 중요한 철학적 입장의 차이가 있었다. 만약 우리가 라이헨바흐의 과학철학적 입장을 카르납과 비견될 만한 논리경험주의의 중요한 인식론적 입장이라고 간주한다면, (...) 과연 그의 입장이 이후 논리경험주의에 대해 제시된 각종 비판을 견딜 수 있는지 다시 점검해 볼 필요가 있다. 이를 위해 우선 나는 논리경험주의의 입장과 이에 대한 비판을 체계적으로 정리하는 과학철학자 수피(Suppe)의 논의를 검토한 후, 논리경험주의에 대한 후대 철학자들의 비판이 결정적이지는 않았음을 보인다. 다음으로 나는 ‘과학적 철학’ 개념, ‘발견의 맥락’과 ‘정당화의 맥락’ 구분, ‘과학 이론의 합리적 재구성’, ‘과학자와 철학자의 노동 분업’ 등 논리경험주의의 주요 인식론적 논제에 관한 라이헨바흐의 입장을 재구성한다. 이러한 재구성을 통해 나는, 라이헨바흐의 인식론적 입장이 구체적인 과학 이론의 인식론적 의의와 함축을 도출해내는데 있어 여전히 유효한 입장이라는 것을 보일 것이다. 실제로 라이헨바흐가 주장한 ‘이론 구체적인 인식론적 분석’은 오늘날에도 여전히 유용하고 필요한 철학적 방법론이며, 이 방법론은 논리경험주의에 반대하면서 얻어진 것이 아니라 논리경험주의가 오늘날의 과학철학에 남긴 소중한 유산이라고 보아야 한다. (shrink)

In this essay, I argue for a view that inclusive positivists share with Ronald Dworkin. According to the Moral Incorporation Thesis (MIT), it is logically possible for a legal system to incorporate moral criteria of legality (or “grounds of law,” as Dworkin puts it). Up to this point, the debate has taken the shape of attacks on the coherence of MIT with the defender of MIT merely attempting to refute the attacking argument. I give a positive argument for MIT. (...) I begin with an explanation of the logic of establishing possibility claims, such as MIT. At the outset, it is worth noting that the logic of establishing possibility claims is very different from the logic of establishing contingent descriptive claims or necessary claims. For this reason, some explication of the relevant features of the semantics of modal logic will be necessary here. Once the structural framework is adequately developed, the argument for MIT will be grounded on the strength of a thought experiment of a surprisingly simple kind. Indeed, the argument is inspired by a Razian argument for the possibility of a legal system without coercive enforcement machinery; on his view, a society of angels could still have a system of law without any coercive machinery. My argument will possess two theoretically important qualities that are also possessed by Raz’s powerfully simple, but ultimately unsuccessful, argument. (shrink)

One is tempted to look upon the positive and the logical somewhat as one looks upon the quick and the dead. Yet the issue is hardly that sharp. Viability has strange possibilities and varied forms, and must often be appraised with an eye directed as much towards the environment as towards the claimant organism. Stretching the application of the word ‘viable’ to complexes of behavior such as the philosophies and theories of knowledge, we may ask: Is the combination of (...) the positive and the logical in logical positivism viable? And is this logical positivism itself as it stands either positive or logical? (shrink)

This paper presents rules of inference for a binary quantifier I for the formalisation of sentences containing definite descriptions within intuitionist positive free logic. I binds one variable and forms a formula from two formulas. Ix[F, G] means ‘The F is G’. The system is shown to have desirable proof-theoretic properties: it is proved that deductions in it can be brought into normal form. The discussion is rounded up by comparisons between the approach to the formalisation of definite (...) descriptions recommended here and the more usual approach that uses a term-forming operator ι, where ιxF means ‘the F’. (shrink)

Ten brilliant essays on logic appear in this collection, the work of one of the world’s best-known authorities on logic. In these thought-provoking arguments and meditations, Nobel Prize winner Bertrand Russell challenges the romantic mysticism of the 19th century, positing instead his theory of logical atomism. These essays are categorized by Russell as "entirely popular" and "somewhat more technical." The former include the well-known title essay plus "A Free Man’s Worship" and "The Place of Science in a Liberal (...) Education"; the latter comprise "On the Notion of Cause" and "Knowledge by Acquaintance and Knowledge by Description," along with other essays written in the cogent and witty style for which their author is justly renowned. (shrink)