Propositional Logic [Internet Encyclopedia of Philosophy]
Total Page:16
File Type:pdf, Size:1020Kb

Load more
Recommended publications
-
Chapter 5: Methods of Proof for Boolean Logic
Chapter 5: Methods of Proof for Boolean Logic § 5.1 Valid inference steps Conjunction elimination Sometimes called simplification. From a conjunction, infer any of the conjuncts. • From P ∧ Q, infer P (or infer Q). Conjunction introduction Sometimes called conjunction. From a pair of sentences, infer their conjunction. • From P and Q, infer P ∧ Q. § 5.2 Proof by cases This is another valid inference step (it will form the rule of disjunction elimination in our formal deductive system and in Fitch), but it is also a powerful proof strategy. In a proof by cases, one begins with a disjunction (as a premise, or as an intermediate conclusion already proved). One then shows that a certain consequence may be deduced from each of the disjuncts taken separately. One concludes that that same sentence is a consequence of the entire disjunction. • From P ∨ Q, and from the fact that S follows from P and S also follows from Q, infer S. The general proof strategy looks like this: if you have a disjunction, then you know that at least one of the disjuncts is true—you just don’t know which one. So you consider the individual “cases” (i.e., disjuncts), one at a time. You assume the first disjunct, and then derive your conclusion from it. You repeat this process for each disjunct. So it doesn’t matter which disjunct is true—you get the same conclusion in any case. Hence you may infer that it follows from the entire disjunction. In practice, this method of proof requires the use of “subproofs”—we will take these up in the next chapter when we look at formal proofs. -
The Incorrect Usage of Propositional Logic in Game Theory
The Incorrect Usage of Propositional Logic in Game Theory: The Case of Disproving Oneself Holger I. MEINHARDT ∗ August 13, 2018 Recently, we had to realize that more and more game theoretical articles have been pub- lished in peer-reviewed journals with severe logical deficiencies. In particular, we observed that the indirect proof was not applied correctly. These authors confuse between statements of propositional logic. They apply an indirect proof while assuming a prerequisite in order to get a contradiction. For instance, to find out that “if A then B” is valid, they suppose that the assumptions “A and not B” are valid to derive a contradiction in order to deduce “if A then B”. Hence, they want to establish the equivalent proposition “A∧ not B implies A ∧ notA” to conclude that “if A then B”is valid. In fact, they prove that a truth implies a falsehood, which is a wrong statement. As a consequence, “if A then B” is invalid, disproving their own results. We present and discuss some selected cases from the literature with severe logical flaws, invalidating the articles. Keywords: Transferable Utility Game, Solution Concepts, Axiomatization, Propositional Logic, Material Implication, Circular Reasoning (circulus in probando), Indirect Proof, Proof by Contradiction, Proof by Contraposition, Cooperative Oligopoly Games 2010 Mathematics Subject Classifications: 03B05, 91A12, 91B24 JEL Classifications: C71 arXiv:1509.05883v1 [cs.GT] 19 Sep 2015 ∗Holger I. Meinhardt, Institute of Operations Research, Karlsruhe Institute of Technology (KIT), Englerstr. 11, Building: 11.40, D-76128 Karlsruhe. E-mail: [email protected] The Incorrect Usage of Propositional Logic in Game Theory 1 INTRODUCTION During the last decades, game theory has encountered a great success while becoming the major analysis tool for studying conflicts and cooperation among rational decision makers. -
46. on the Completeness O F the Leibnizian Modal System with a Restriction by Setsuo SAITO Shibaura Institute of Technology,Tokyo (Comm
198 [Vol. 42, 46. On the Completeness o f the Leibnizian Modal System with a Restriction By Setsuo SAITO Shibaura Institute of Technology,Tokyo (Comm. by Zyoiti SUETUNA,M.J.A., March 12, 1966) § 1. Introduction. The purpose of this paper is to show the completeness of a modal system which will be called Lo in the following. In my previous paper [1], in order to show an example of defence of _.circular definition, the following definition was given: A statement is analytic if and only if it is consistent with every statement that expresses what is possible. This definition, roughly speaking, is materially equivalent to Carnap's definition of L-truth which is suggested by Leibniz' conception that a necessary truth must hold in all possible worlds (cf. Carnap [2], p.10). If "analytic" is replaced by "necessary" in the above definition, this definition becomes as follows: A statement is necessary if and only if it is consistent with every statement that expresses what is possible. This reformed definition is symbolized by modal signs as follows: Opm(q)[Qq~O(p•q)1, where p and q are propositional variables. Let us replace it by the following axiom-schema and rule: Axiom-schema. D a [Q,9 Q(a •,S)], where a, ,9 are arbitrary formulas. Rule of inference. If H Q p Q(a •p), then i- a, where a is an arbitrary formula and p is a propositional variable not contained in a. We call L (the Leibnizian modal system) the system obtained from the usual propositional calculus by adding the above axiom schema and rule and the rule of replacement of material equivalents. -
Propositional Logic
Chapter 3 Propositional Logic 3.1 ARGUMENT FORMS This chapter begins our treatment of formal logic. Formal logic is the study of argument forms, abstract patterns of reasoning shared by many different arguments. The study of argument forms facilitates broad and illuminating generalizations about validity and related topics. We shall initially focus on the notion of deductive validity, leaving inductive arguments to a later treatment (Chapters 8 to 10). Specifically, our concern in this chapter will be with the idea that a valid deductive argument is one whose conclusion cannot be false while the premises are all true (see Section 2.3). By studying argument forms, we shall be able to give this idea a very precise and rigorous characterization. We begin with three arguments which all have the same form: (1) Today is either Monday or Tuesday. Today is not Monday. Today is Tuesday. (2) Either Rembrandt painted the Mona Lisa or Michelangelo did. Rembrandt didn't do it. :. Michelangelo did. (3) Either he's at least 18 or he's a juvenile. He's not at least 18. :. He's a juvenile. It is easy to see that these three arguments are all deductively valid. Their common form is known by logicians as disjunctive syllogism, and can be represented as follows: Either P or Q. It is not the case that P :. Q. The letters 'P' and 'Q' function here as placeholders for declarative' sentences. We shall call such letters sentence letters. Each argument which has this form is obtainable from the form by replacing the sentence letters with sentences, each occurrence of the same letter being replaced by the same sentence. -
Natural Deduction with Propositional Logic
Natural Deduction with Propositional Logic Introducing Natural Natural Deduction with Propositional Logic Deduction Ling 130: Formal Semantics Some basic rules without assumptions Rules with assumptions Spring 2018 Outline Natural Deduction with Propositional Logic Introducing 1 Introducing Natural Deduction Natural Deduction Some basic rules without assumptions 2 Some basic rules without assumptions Rules with assumptions 3 Rules with assumptions What is ND and what's so natural about it? Natural Deduction with Natural Deduction Propositional Logic A system of logical proofs in which assumptions are freely introduced but discharged under some conditions. Introducing Natural Deduction Introduced independently and simultaneously (1934) by Some basic Gerhard Gentzen and Stanis law Ja´skowski rules without assumptions Rules with assumptions The book & slides/handouts/HW represent two styles of one ND system: there are several. Introduced originally to capture the style of reasoning used by mathematicians in their proofs. Ancient antecedents Natural Deduction with Propositional Logic Aristotle's syllogistics can be interpreted in terms of inference rules and proofs from assumptions. Introducing Natural Deduction Some basic rules without assumptions Rules with Stoic logic includes a practical application of a ND assumptions theorem. ND rules and proofs Natural Deduction with Propositional There are at least two rules for each connective: Logic an introduction rule an elimination rule Introducing Natural The rules reflect the meanings (e.g. as represented by Deduction Some basic truth-tables) of the connectives. rules without assumptions Rules with Parts of each ND proof assumptions You should have four parts to each line of your ND proof: line number, the formula, justification for writing down that formula, the goal for that part of the proof. -
Chapter 10: Symbolic Trails and Formal Proofs of Validity, Part 2
Essential Logic Ronald C. Pine CHAPTER 10: SYMBOLIC TRAILS AND FORMAL PROOFS OF VALIDITY, PART 2 Introduction In the previous chapter there were many frustrating signs that something was wrong with our formal proof method that relied on only nine elementary rules of validity. Very simple, intuitive valid arguments could not be shown to be valid. For instance, the following intuitively valid arguments cannot be shown to be valid using only the nine rules. Somalia and Iran are both foreign policy risks. Therefore, Iran is a foreign policy risk. S I / I Either Obama or McCain was President of the United States in 2009.1 McCain was not President in 2010. So, Obama was President of the United States in 2010. (O v C) ~(O C) ~C / O If the computer networking system works, then Johnson and Kaneshiro will both be connected to the home office. Therefore, if the networking system works, Johnson will be connected to the home office. N (J K) / N J Either the Start II treaty is ratified or this landmark treaty will not be worth the paper it is written on. Therefore, if the Start II treaty is not ratified, this landmark treaty will not be worth the paper it is written on. R v ~W / ~R ~W 1 This or statement is obviously exclusive, so note the translation. 427 If the light is on, then the light switch must be on. So, if the light switch in not on, then the light is not on. L S / ~S ~L Thus, the nine elementary rules of validity covered in the previous chapter must be only part of a complete system for constructing formal proofs of validity. -
Propositional Team Logics
Propositional Team Logics✩ Fan Yanga,1,∗, Jouko V¨a¨an¨anenb,2 aDepartment of Values, Technology and Innovation, Delft University of Technology, Jaffalaan 5, 2628 BX Delft, The Netherlands bDepartment of Mathematics and Statistics, Gustaf H¨allstr¨omin katu 2b, PL 68, FIN-00014 University of Helsinki, Finland and University of Amsterdam, The Netherlands Abstract We consider team semantics for propositional logic, continuing[34]. In team semantics the truth of a propositional formula is considered in a set of valuations, called a team, rather than in an individual valuation. This offers the possibility to give meaning to concepts such as dependence, independence and inclusion. We associate with every formula φ based on finitely many propositional variables the set JφK of teams that satisfy φ. We define a full propositional team logic in which every set of teams is definable as JφK for suitable φ. This requires going beyond the logical operations of classical propositional logic. We exhibit a hierarchy of logics between the smallest, viz. classical propositional logic, and the full propositional team logic. We characterize these different logics in several ways: first syntactically by their logical operations, and then semantically by the kind of sets of teams they are capable of defining. In several important cases we are able to find complete axiomatizations for these logics. Keywords: propositional team logics, team semantics, dependence logic, non-classical logic 2010 MSC: 03B60 1. Introduction In classical propositional logic the propositional atoms, say p1,...,pn, are given a truth value 1 or 0 by what is called a valuation and then any propositional formula φ can be associated with the set |φ| of valuations giving φ the value 1. -
Inversion by Definitional Reflection and the Admissibility of Logical Rules
THE REVIEW OF SYMBOLIC LOGIC Volume 2, Number 3, September 2009 INVERSION BY DEFINITIONAL REFLECTION AND THE ADMISSIBILITY OF LOGICAL RULES WAGNER DE CAMPOS SANZ Faculdade de Filosofia, Universidade Federal de Goias´ THOMAS PIECHA Wilhelm-Schickard-Institut, Universitat¨ Tubingen¨ Abstract. The inversion principle for logical rules expresses a relationship between introduction and elimination rules for logical constants. Hallnas¨ & Schroeder-Heister (1990, 1991) proposed the principle of definitional reflection, which embodies basic ideas of inversion in the more general context of clausal definitions. For the context of admissibility statements, this has been further elaborated by Schroeder-Heister (2007). Using the framework of definitional reflection and its admis- sibility interpretation, we show that, in the sequent calculus of minimal propositional logic, the left introduction rules are admissible when the right introduction rules are taken as the definitions of the logical constants and vice versa. This generalizes the well-known relationship between introduction and elimination rules in natural deduction to the framework of the sequent calculus. §1. Inversion principle. The idea of inverting logical rules can be found in a well- known remark by Gentzen: “The introductions are so to say the ‘definitions’ of the sym- bols concerned, and the eliminations are ultimately only consequences hereof, what can approximately be expressed as follows: In eliminating a symbol, the formula concerned – of which the outermost symbol is in question – may only ‘be used as that what it means on the ground of the introduction of that symbol’.”1 The inversion principle itself was formulated by Lorenzen (1955) in the general context of rule-based systems and is thus not restricted to logical rules. -
Logical Inference and Its Dynamics
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by PhilPapers Logical Inference and Its Dynamics Carlotta Pavese 1 Duke University Philosophy Department Abstract This essay advances and develops a dynamic conception of inference rules and uses it to reexamine a long-standing problem about logical inference raised by Lewis Carroll's regress. Keywords: Inference, inference rules, dynamic semantics. 1 Introduction Inferences are linguistic acts with a certain dynamics. In the process of making an inference, we add premises incrementally, and revise contextual assump- tions, often even just provisionally, to make them compatible with the premises. Making an inference is, in this sense, moving from one set of assumptions to another. The goal of an inference is to reach a set of assumptions that supports the conclusion of the inference. This essay argues from such a dynamic conception of inference to a dynamic conception of inference rules (section x2). According to such a dynamic con- ception, inference rules are special sorts of dynamic semantic values. Section x3 develops this general idea into a detailed proposal and section x4 defends it against an outstanding objection. Some of the virtues of the dynamic con- ception of inference rules developed here are then illustrated by showing how it helps us re-think a long-standing puzzle about logical inference, raised by Lewis Carroll [3]'s regress (section x5). 2 From The Dynamics of Inference to A Dynamic Conception of Inference Rules Following a long tradition in philosophy, I will take inferences to be linguistic acts. 2 Inferences are acts in that they are conscious, at person-level, and 1 I'd like to thank Guillermo Del Pinal, Simon Goldstein, Diego Marconi, Ram Neta, Jim Pryor, Alex Rosenberg, Daniel Rothschild, David Sanford, Philippe Schlenker, Walter Sinnott-Armstrong, Seth Yalcin, Jack Woods, and three anonymous referees for helpful suggestions on earlier drafts. -
Accepting a Logic, Accepting a Theory
1 To appear in Romina Padró and Yale Weiss (eds.), Saul Kripke on Modal Logic. New York: Springer. Accepting a Logic, Accepting a Theory Timothy Williamson Abstract: This chapter responds to Saul Kripke’s critique of the idea of adopting an alternative logic. It defends an anti-exceptionalist view of logic, on which coming to accept a new logic is a special case of coming to accept a new scientific theory. The approach is illustrated in detail by debates on quantified modal logic. A distinction between folk logic and scientific logic is modelled on the distinction between folk physics and scientific physics. The importance of not confusing logic with metalogic in applying this distinction is emphasized. Defeasible inferential dispositions are shown to play a major role in theory acceptance in logic and mathematics as well as in natural and social science. Like beliefs, such dispositions are malleable in response to evidence, though not simply at will. Consideration is given to the Quinean objection that accepting an alternative logic involves changing the subject rather than denying the doctrine. The objection is shown to depend on neglect of the social dimension of meaning determination, akin to the descriptivism about proper names and natural kind terms criticized by Kripke and Putnam. Normal standards of interpretation indicate that disputes between classical and non-classical logicians are genuine disagreements. Keywords: Modal logic, intuitionistic logic, alternative logics, Kripke, Quine, Dummett, Putnam Author affiliation: Oxford University, U.K. Email: [email protected] 2 1. Introduction I first encountered Saul Kripke in my first term as an undergraduate at Oxford University, studying mathematics and philosophy, when he gave the 1973 John Locke Lectures (later published as Kripke 2013). -
A Sequent System for LP
A Sequent System for LP Gladys Palau1 , Carlos A. Oller1 1 Facultad de Filosofía y Letras, Universidad de Buenos Aires Facultad de Humanidades y Ciencias de la Educación, Universidad Nacional de La Plata [email protected] ; [email protected] Abstract. This paper presents a Gentzen-type sequent system for Priest s three- valued paraconsistent logic LP. This sequent system is not canonical because it introduces non-standard axioms. Furthermore, the rules for the conditional and negation connectives are not the classical ones. Some philosophical consequences of this type of sequent presentation for many-valued logics are discussed. 1 Introduction This paper introduces a sequent system for Priest s many-valued and paraconsistent logic LP (Logic of Paradox)[6]. Priest presents this logic to deal with paradoxes, vague contexts and the alleged existence of true contradictions or dialetheias. A logic is paraconsistent if and only if its consequence relation is paraconsistent, and a consequence relation is paraconsistent if and only if it is not explosive. A consequence relation ├ is explosive if and only if, for any formulas A and B, {A, ¬A} ├ B (ECQ). In addition, Priest's logic LP is a three-valued system in which both a formula as its negation can receive a designated truth value. In his 1979 paper and in [7 ], [ 8 ] and [ 9 ] Priest offers a semantic characterization of LP. He also offers a natural deduction formulation of LP in [9]. Anthony Bloesch provides in [3] a formulation of LP as a system of signed tableaux and Tony Roy offers in [10] another presentation of LP as a natural deduction system. -
Introduction to Logic 1
Introduction to logic 1. Logic and Artificial Intelligence: some historical remarks One of the aims of AI is to reproduce human features by means of a computer system. One of these features is reasoning. Reasoning can be viewed as the process of having a knowledge base (KB) and manipulating it to create new knowledge. Reasoning can be seen as comprised of 3 processes: 1. Perceiving stimuli from the environment; 2. Translating the stimuli in components of the KB; 3. Working on the KB to increase it. We are going to deal with how to represent information in the KB and how to reason about it. We use logic as a device to pursue this aim. These notes are an introduction to modern logic, whose origin can be found in George Boole’s and Gottlob Frege’s works in the XIX century. However, logic in general traces back to ancient Greek philosophers that studied under which conditions an argument is valid. An argument is any set of statements – explicit or implicit – one of which is the conclusion (the statement being defended) and the others are the premises (the statements providing the defense). The relationship between the conclusion and the premises is such that the conclusion follows from the premises (Lepore 2003). Modern logic is a powerful tool to represent and reason on knowledge and AI has traditionally adopted it as working tool. Within logic, one research tradition that strongly influenced AI is that started by the German philosopher and mathematician Gottfried Leibniz. His aim was to formulate a Lingua Rationalis to create a universal language based only on rationality, which could solve all the controversies between different parties.