scholarly journals Modal Mantık'ta 'Strict Implication-Material Implication' (Sıkı Gerektirme-Maddi Gerektirme) Teorisi

2003 ◽  
Vol 44 (1) ◽  
pp. 1
Author(s):  
KÖZ İsmail
Keyword(s):  
Strict Implication ◽  
Material Implication

Extensions of the Lewis system S5

1951 ◽  
Vol 16 (2) ◽  
pp. 112-120 ◽  
Author(s):  
Schiller Joe Scroggs
Keyword(s):  
Broad Class ◽  
Characteristic Matrix ◽  
Normal Extension ◽  
Strict Implication ◽  
Finite Characteristic ◽  
Material Implication ◽  
Sentential Calculus ◽  
The Third ◽  
Simple Class ◽  
Definition Of

Dugundji has proved that none of the Lewis systems of modal logic, S1 through S5, has a finite characteristic matrix. The question arises whether there exist proper extensions of S5 which have no finite characteristic matrix. By an extension of a sentential calculus S, we usually refer to any system S′ such that every formula provable in S is provable in S′. An extension S′ of S is called proper if it is not identical with S. The answer to the question is trivially affirmative in case we make no additional restrictions on the class of extensions. Thus the extension of S5 obtained by adding to the provable formulas the additional formula p has no finite characteristic matrix (indeed, it has no characteristic matrix at all), but this extension is not closed under substitution—the formula q is not provable in it. McKinsey and Tarski have defined normal extensions of S4* by imposing three conditions. Normal extensions must be closed under substitution, must preserve the rule of detachment under material implication, and must also preserve the rule that if α is provable then ~◊~α is provable. McKinsey and Tarski also gave an example of an extension of S4 which satisfies the first two of these conditions but not the third. One of the results of this paper is that every extension of S5 which satisfies the first two of these conditions also satisfies the third, and hence the above definition of normal extension is redundant for S5. We shall therefore limit the extensions discussed in this paper to those which are closed under substitution and which preserve the rule of detachment under material implication. These extensions we shall call quasi-normal. The class of quasi-normal extensions of S5 is a very broad class and actually includes all extensions which are likely to prove interesting. It is easily shown that quasi-normal extensions of S5 preserve the rules of replacement, adjunction, and detachment under strict implication. It is the purpose of this paper to prove that every proper quasi-normal extension of S5 has a finite characteristic matrix and that every quasi-normal extension of S5 is a normal extension of S5 and to describe a simple class of characteristic matrices for S5.

On the interpretation of the sign ‘⊃’

1953 ◽  
Vol 18 (1) ◽  
pp. 60-62 ◽  
Author(s):  
John Myhill
Keyword(s):  
The Other ◽  
Strict Implication ◽  
Material Implication ◽  
Strict Interpretation ◽  
False Proposition ◽  
Positive Logic ◽  
Law Of Excluded Middle ◽  
Image Position ◽  
Formal Fallacies ◽  
Excluded Middle

The sign ‘⊃’ (or ‘→’ or ‘C’) functions in many logical systems in a way which precludes its interpretation as either strict or material implication. For example, in the systems of Heyting, Johansson, Fitch and Bernays (positive logic), the following are theorems:Now if ‘⊃’ were interpreted as strict implication, ⊃2 would mean ‘if p is true, then p is strictly implied by every proposition’, i.e. ‘if p is true, it is necessarily true’, which is false for contingently true p. If on the other hand ‘⊃’ were interpreted as material implication, ⊃1 would reduce to ‘~p ∨ p’, i.e. to the law of excluded middle, which is conspicuously lacking in the systems mentioned. The reader is likely in practice to veer between these two interpretations. Thus in Fitch or Heyting on realizing that ‘~p⊃▪ p⊃q’ is a theorem, one thinks of it as meaning ‘a false proposition implies everything’ and regards the implication as material; but the presence of ‘p⊃p’ as a theorem, even for choices of p which do not satisfy excluded middle, inclines one again to the strict interpretation. This vacillation, while it need not lead to the commission of any formal fallacies, tends to hamstring one's intuition and thus waste time. The purpose of this paper is to suggest an interpretation of ‘⊃’ which will prevent such havering.Let two formulae A and B be called interdeducible if A ⊢ B and B ⊢ A.

Independent axiom schemata for S5

1956 ◽  
Vol 21 (3) ◽  
pp. 255-256
Author(s):  
Alan Ross Anderson
Keyword(s):  
Strict Implication ◽  
Material Implication ◽  
Independent Axiom ◽  
Image Position

Leo Simons has shown that H1—H6 below constitute a set of independent axiom schemata for S3, with detachment for material implication “→” as the only primitive rule. He also showed that addition of the scheme (◇ ◇ α ⥽ ◇ α) yields S4, and that these schemata for S4 are independent. The question for S5 was left open. We shall show (presupposing familiarity with Simons' paper) that H1—H6 and S, below, constitute a set of independent axiom schemata for S5, with detachment for material implication as the only primitive rule.Let S5′ be the system generated from H1—H6 and S with the help of the primitive rule. It is easy to see that Simons' derivations of the rules (a) adjunction, (b) detachment for strict implication, and (c) intersubstitutability of strict equivalents, may be carried out for S5′. We know that (1) (∼ ◇ ∼ α ⥽ ◇ α) is provable in S2, hence also in S3 and S5′; and (1) and S yield (2) (α ⥽ ∼ ◇ ∼ ◇ α). Perry has shown that addition of (2) to S3 yields S5, so S5 is a subsystem of S5′. And it is easy to prove S in S5; hence the systems are equivalent.

scholarly journals Super-Strict Implications

2021 ◽  
Author(s):  
Eugenio Orlandelli ◽  
Guido Gherardi
Keyword(s):  
Modal Logics ◽  
Relational Semantics ◽  
Strict Implication ◽  
Material Implication ◽  
Structural Rules ◽  
Relational Frames

This paper introduces the logics of super-strict implications, where  a super-strict implication is  a strengthening of  C.I. Lewis' strict implication that avoids not only the paradoxes of material implication but also those of strict implication. The semantics of super-strict implications is obtained by strengthening the (normal) relational semantics for strict implication. We consider all logics of super-strict implications that are based on relational frames for modal logics in the  modal cube. it is shown that all  logics of super-strict implications are connexive logics in that they validate Aristotle's Theses and (weak) Boethius's Theses. A proof-theoretic characterisation of logics of super-strict implications is given by means of G3-style labelled calculi, and it is proved that the structural rules of inference are admissible in these calculi. It  is also shown that validity in the $$\mathsf{S5}$$-based logic of super-strict implications is equivalent to validity in  G. Priest's negation-as-cancellation-based  logic. Hence, we also   give a cut-free calculus for Priest's logic.

Note on a recent set of postulates for the calculus of propositions

1939 ◽  
Vol 4 (1) ◽  
pp. 10-14 ◽  
Author(s):  
K. V. Huntington
Keyword(s):  
American Academy ◽  
Essential Difference ◽  
Strict Implication ◽  
Material Implication ◽  
Logical Deduction ◽  
Indefinite Number

In my American Academy paper of 1937 I gave a mathematical clarification and extension of C. I. Lewis's theory of strict implication using as the base (K, T, ×, ′, ≣). In that paper the element a⊰b (read “a hook b”) was defined by (a⊰b) = (ab′=cc′). The main purpose of the present paper is to show that this definition may be replaced by the simpler definition (a⊰b) = (ab≣a), provided Postulate 15 is replaced by two simpler postulates, 15a and 15b (see below). The paper may also serve to throw further light on the essential difference between Lewis's theory of “strict” implication and the more familiar theory of “material” implication. This paper and the earlier one, when read together, are entirely self-contained, all proofs (including proofs of independence) being given in full and no reference to earlier literature being required.We begin by reviewing briefly the rôle which logical deduction plays in the writing of any scientific book.Suppose you sit down to write. What do you actually do? In the last analysis, your activity as an author is a process of voluntary selection, restricted by certain inescapable rules. From an indefinite number of possible propositions which may occur to your imagination, you voluntarily select certain propositions which you accept as being worthy of being written down, one after another, in your book. Every proposition which occurs to you is either accepted, or rejected, or laid aside for further consideration.

VI.—IS MATERIAL IMPLICATION INFERENTIALLY HARMLESS?

Mind ◽  
1966 ◽  
Vol LXXV (300) ◽  
pp. 542-551 ◽  
Author(s):  
J. O. NELSON
Keyword(s):  
Material Implication

On the logic of incomplete answers

1965 ◽  
Vol 30 (1) ◽  
pp. 65-68 ◽  
Author(s):  
M. J. Cresswell
Keyword(s):  
Formal Analysis ◽  
Complete List ◽  
Strict Implication ◽  
Complete Answer ◽  
Questions And Answers ◽  
Image Position

I have argued in [1] that a concept bearing some resemblance to ‘p is the answer to d’ (p a proposition and d a question) can be defined wherever d has the form,‘For which a's is it the case that A (a)?’ (Qa)A(a)where a is a variable and A a wff containing a. To say that p is the true and complete answer to (Qa)A(a) is expressed as saying that p is logically equivalent to the true conjunction of A(a) or ~A(a) for each a. It is defined as;Such a concept of answer is like Belnap's [2] direct true answer to a complete list question, or like Harrah's use [3] (p. 43) of the notion of a state description. The main difference between my approach and that of Belnap and Harrah is that while they are concerned to develop a formal metalanguage for discussion of questions and answers I am concerned to express, as far as possible in existing systems, certain interrogative statements; in particular statements of the form ‘— is the (an) answer to —’.While the account in [1] does give a formal analysis of one ‘answer’ concept there are respects in which it is inadequate.1. Since it uses entailment (or strict implication) to define the relation between p the answer and d the question we can shew that if p is the answer to d and q is logically equivalent to p then q is the answer to d.

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