This introduction to mathematical logic starts with propositional calculus and first-order logic. Topics covered include syntax, semantics, soundness, completeness, independence, normal forms, vertical paths through negation normal formulas, compactness, Smullyan's Unifying Principle, natural deduction, cut-elimination, semantic tableaux, Skolemization, Herbrand's Theorem, unification, duality, interpolation, and definability. The last three chapters of the book provide an introduction to type theory (higher-order logic). It is shown how various mathematical concepts can be formalized in this very expressive formal language. This expressive notation facilitates proofs (...) of the classical incompleteness and undecidability theorems which are very elegant and easy to understand. The discussion of semantics makes clear the important distinction between standard and nonstandard models which is so important in understanding puzzling phenomena such as the incompleteness theorems and Skolem's Paradox about countable models of set theory. Some of the numerous exercises require giving formal proofs. A computer program called ETPS which is available from the web facilitates doing and checking such exercises. Audience: This volume will be of interest to mathematicians, computer scientists, and philosophers in universities, as well as to computer scientists in industry who wish to use higher-order logic for hardware and software specification and verification. (shrink)

Elizabeth Anscombe is among the most distinguished and original philosophers alive today. Her work has ranged over many areas of philosophy, including metaphysics, ethics, the philosophy of mind and action, and the philosophy of religion. In each of these areas she has made seminal contributions. The essays in this book reflect the breadth of her interests and the esteem in which she is held by her colleagues. The distinguished contributors include Michael Dunnett, Nancy Cartwright, Peter Geach and Philippa Foot; and (...) Professor Anscombe's essay 'Making True' is published here for the first time. (shrink)

It is sometimes said that there are two, competing versions of W. V. O. Quine’s unrelenting empiricism, perhaps divided according to temporal periods of his career. According to one, logic is exempt from, or lies outside the scope of, the attack on the analytic-synthetic distinction. This logic-friendly Quine holds that logical truths and, presumably, logical inferences are analytic in the traditional sense. Logical truths are knowable a priori, and, importantly, they are incorrigible, and so immune from revision. The other, radical (...) reading of Quine does not exempt logic from the attack on analyticity and a priority. Logical truths and inferences are themselves part of the web of belief, and the same global methodology applies to logic as to any other part of the web, such as theoretical chemistry or ordinary beliefs about ordinary objects. Everything, including logic, is up for grabs in our struggle for holistic confirmation. The purpose of this paper is to examine the law of non-contradiction, and the concomitant principle of ex falso quodlibet, from the perspective of the principles advocated by the radical Quine. I show that he has no compelling reason to accept either of these. To put it bluntly, neither the law of non-contradiction nor the rule of ex falso quodlibet is empirically confirmed, and these principles fare poorly on the various criteria for theory acceptance on the methodology of the radical Quine. So the radical Quine is led rather quickly and rather directly into something in the neighborhood of Graham Priest’s dialetheism. (shrink)

Background ideas -- Consequences -- Relations of support -- Logical consequence : the basic recipe -- Valid arguments and truth -- Language, form, and logical theories -- Language -- Atoms, connectives, and molecules -- Connectives and form -- Validity and form -- Language and formal languages -- Logical theories : rivalry -- Set-theoretic tools -- Sets -- Ordered sets : pairs and n-tuples -- Relations -- Functions -- Sets as tools -- Basic connectives -- Classical theory -- Cases : complete (...) and consistent -- Classical truth conditions -- Basic classical consequence -- Motivation : precision -- Defined connectives -- Some notable valid forms -- A paracomplete theory -- Apparent unsettledness -- Cases : incomplete -- Paracomplete truth and falsity conditions -- Paracomplete consequence -- Defined connectives -- Some notable forms -- A paraconsistent theory -- Apparent overdeterminacy -- Cases : inconsistent -- Paraconsistent truth conditions -- Paraconsistent consequence -- Defined connectives -- Some notable forms -- Innards, identity, and quantifiers -- Atomic innards -- Atomic innards : names and predicates -- Truth and falsity conditions for atomics -- Cases, domains, and interpretation functions -- Classical, paracomplete, and paraconsistent -- Identity -- Logical expressions and logical form -- Validity involving identity -- Identity : informal sketch -- Truth conditions : informal sketch -- Everything and something -- Validity involving quantifiers -- Quantifiers : an informal sketch -- Truth and falsity conditions -- Paraconsistent, paracomplete, classical -- Freedom, necessity, and beyond -- Speaking freely -- Speaking of non-existent things -- Existential import -- Freeing our terms, expanding our domains -- Truth conditions : an informal sketch -- Possibilities -- Possibility and necessity -- Towards truth and falsity conditions -- Cases and consequence -- Remark on going beyond possibility -- Glimpsing different logical roads -- Other conditionals -- Other negations -- Other alethic modalities : actuality -- Same connectives, different truth conditions -- Another road to difference : consequence. (shrink)

of Γ, {X, Y } is simultaneously satisfiable. 2. Given that Γ and ∆ are simultaneously satisfiable, would Π = Γ ∩ ∆ be simultaneously satisfiable? 3. Prove the following results: (a) {A ⊃ B, ¬A ⊃ B} B. (b) A ∨ B B ∨ A. (c) ¬(A ∧ ¬A). 4. Find a disjunctive normal form for the formula (B ∧ C) ⊃ (A ↔ (¬B ∨ C)). 5. Show that the formula:    Ai..

There is a principle in things, about which we cannot be deceived, but must always, on the contrary, recognize the truth – viz. that the same thing cannot at one and the same time be and not be": with these words of the Metaphysics, Aristotle introduced the Law of Non-Contradiction, which was to become the most authoritative principle in the history of Western thought. However, things have recently changed, and nowadays various philosophers, called dialetheists, claim that this Law does not (...) hold unrestrictedly – that in peculiar circumstances the same thing may at the same time be and not be, and contradictions may obtain in the world. This book opens with an examination of the famous logical paradoxes that appear to speak on behalf of contradictions (e.g., the Liar paradox, the set-theoretic paradoxes such as Cantor’s and Russell’s), and of the reasons for the failure of the standard attempts to solve them. It provides, then, an introduction to paraconsistent logics – non-classical logics in which the admission of contradictions does not lead to logical chaos –, and their astonishing applications, going from inconsistent data base management to contradictory arithmetics capable of circumventing Gödel’s celebrated Incompleteness Theorem. The final part of the book discusses the philosophical motivations and difficulties of dialetheism, and shows how to extract from Aristotle’s ancient words a possible reply to the dialetheic challenge. How to Sell a Contradiction will appeal to anyone interested in non-classical logics, analytic metaphysics, and philosophy of mathematics, and especially to those who consider challenging our most entrenched beliefs the main duty of philosophical inquiry. (shrink)

Describes the received theory of necessary and sufficient conditions, explains some standard objections to it, and lays out alternative ways of thinking about conditions and conditionals.

The work is the presentation of a logical theory - Logic in Reality (LIR) - and of applications of that theory in natural science and philosophy, including ...

Book review r A. (2004). "Book review: Yves nievergelt, foundations of ...

Introduction This is an elementary logic book designed for people who have no technical familiarity with modern logic but who have been reasoning, ...

Assuming no previous study in logic, this informal yet rigorous text covers the material of a standard undergraduate first course in mathematical logic, using natural deduction and leading up to the completeness theorem for first-order logic. At each stage of the text, the reader is given an intuition based on standard mathematical practice, which is subsequently developed with clean formal mathematics. Alongside the practical examples, readers learn what can and can't be calculated; for example the correctness of a derivation proving (...) a given sequent can be tested mechanically, but there is no general mechanical test for the existence of a derivation proving the given sequent. The undecidability results are proved rigorously in an optional final chapter, assuming Matiyasevich's theorem characterising the computably enumerable relations. Rigorous proofs of the adequacy and completeness proofs of the relevant logics are provided, with careful attention to the languages involved. Optinal sections discuss the classification of mathematical structures by first-order theories; the required theory of cardinality is developed from scratch. Throughout the book there are notes on historical aspects of the material, and connections with linguistics and computer science, and the discussion of syntax and semantics is influenced by modern linguistic approaches. Two basic themes in recent cognitive science studies of actual human reasoning are also introduced. Including extensive exercises and selected solutions, this text is ideal for students in logic, mathematics, philosophy, and computer science. (shrink)

This book is intended to be used as a textbook by students of mathematics, and also within limitations as a reference work.

This volume began as a remembrance of Alonzo Church while he was still with us and is now finally complete. It contains papers by many well-known scholars, most of whom have been directly influenced by Church's own work. Often the emphasis is on foundational issues in logic, mathematics, computation, and philosophy - as was the case with Church's contributions, now universally recognized as having been of profound fundamental significance in those areas. The volume will be of interest to logicians, computer (...) scientists, philosophers, and linguists. The contributions concern classical first-order logic, higher-order logic, non-classical theories of implication, set theories with universal sets, the logical and semantical paradoxes, the lambda-calculus, especially as it is used in computation, philosophical issues about meaning and ontology in the abstract sciences and in natural language, and much else. The material will be accessible to specialists in these areas and to advanced graduate students in the respective fields. (shrink)

. In this paper we address the question of recovering a logic system by combining two or more fragments of it. We show that, in general, by fibring two or more fragments of a given logic the resulting logic is weaker than the original one, because some meta-properties of the connectives are lost after the combination process. In order to overcome this problem, the categories Mcon and Seq of multiple-conclusion consequence relations and sequent calculi, respectively, are introduced. The main feature (...) of these categories is the preservation, by morphisms, of meta-properties of the consequence relations, which allows, in several cases, to recover a logic by fibring of its fragments. The fibring in this categories is called meta−fibring. Several examples of well-known logics which can be recovered by meta-fibring its fragments (in opposition to fibring in the usual categories) are given. Finally, a general semantics for objects in Seq (and, in particular, for objects in Mcon) is proposed, obtaining a category of logic systems called Log. A general theorem of preservation of completeness by fibring in Log is also obtained. (shrink)

After a short preface, the first of the three sections of this paper is devoted to historical and philosophic aspects of categoricity. The second section is a self-contained exposition, including detailed definitions, of a proof that every mathematical system whose domain is the closure of its set of distinguished individuals under its distinguished functions is categorically characterized by its induction principle together with its true atoms (atomic sentences and negations of atomic sentences). The third section deals with applications especially those (...) involving the distinction between characterizing a system and axiomatizing the truths of a system. (shrink)

Austin rejects the contention that every proposition has a contradictory. This paper finds problems with the case Austin makes for rejecting the contention in question.

A textbook for an 'advanced introductory' logic class (I used it as a textbook for mathematically capable introductory logic students). The book uses the tableau method, and includes standard results up to a proof of the soundness of predicate logic. Its slightly unusual features include a slightly greater emphasis on decidability than is usual, and more obviously, the presentation of a free logic as standard, alongside a classical alternative. A change of syllabus here means this is no longer under active (...) revision, but I'll leave this archive copy available. (shrink)

This junior/senior level text is devoted to a study of first-order logic and its role in the foundations of mathematics: What is a proof? How can a proof be justified? To what extent can a proof be made a purely mechanical procedure? How much faith can we have in a proof that is so complex that no one can follow it through in a lifetime? The first substantial answers to these questions have only been obtained in this century. The most (...) striking results are contained in Goedel's work: First, it is possible to give a simple set of rules that suffice to carry out all mathematical proofs; but, second, these rules are necessarily incomplete - it is impossible, for example, to prove all true statements of arithmetic. The book begins with an introduction to first-order logic, Goedel's theorem, and model theory. A second part covers extensions of first-order logic and limitations of the formal methods. The book covers several advanced topics, not commonly treated in introductory texts, such as Trachtenbrot's undecidability theorem. Fraissé's elementary equivalence, and Lindstroem's theorem on the maximality of first-order logic. (shrink)

The Snake and the Fox offers students a new and exciting way to look at and understand logic. Mary Haight uses graphics to tell the story of how logic works, and why it works the way it does. This introductory text uses easy to understand language for the student who has no prior understanding of logic or philosophy. The author includes some discussion on the philosophical theory underlying the logic: not just how to do it, but why it takes the (...) form it does. The Snake and the Fox is user-friendly, interactive, uses questions with answers, and has graphics which will easily guide any student coming to logic for the first time. (shrink)

From this starting point, and assuming no previous knowledge of logic, Wilfrid Hodges takes the reader through the whole gamut of logical expressions in a ...

Logic With Trees is a new and original introduction to modern formal logic. It contains discussions on philosophical issues such as truth, conditionals and modal logic, presenting the formal material with clarity, and preferring informal explanations and arguments to intimidatingly rigorous development. Worked examples and exercises guide beginners through the book, with answers to selected exercises enabling readers to check their progress. Logic With Trees equips students with: a complete and clear account of the truth-tree system for first order logic; (...) the importance of logic and its relevance to many different disciplines; the skills to grasp sophisticated formal reasoning techniques necessary to explore complex metalogic; the ability to contest claims that "ordinary" reasoning is well represented by formal first order logic. (shrink)

The idea underlying the Begriffsschrift account of identities was that the content of a sentence is a function of the things it is about. If so, then if an identity a=b is about the content of its contained terms and is true, then a=a and a=b have the same content. But they do not have the same content; so, Frege concluded, identities are not about the contents of their contained terms. The way Frege regarded the matter is that in an (...) identity the terms flanking the symbol for identity do not have their ordinary contents, but instead have themselves as their contents. In 'Uber Sinn und Bedeutung' Frege became convinced that if an identity a=b is about the signs a and b, then it expresses no proper knowledge. So, since it is evident that many such identities do express proper knowledge, Frege concluded that identities are not about their contained signs. So he became convinced that his Begriffsschrift account was incorrect. What was the error in the argument that led Frege to that account? It was thinking that the content of a sentence is a function of the contents of its constituent signs, that is, the things it is about. (shrink)

Prior propounded a theory that, if correct, explains how it is possible for a statement about propositions to be true even if there are no propositions. The major feature of his theory is his treatment of sentence letters as bindable variables in non-referential positions. His theory, however, does not include a semantical account of the resulting quantification. The paper tries to fill that gap.

Preface The most immediate benefit derived from the study of logic is the skill needed to construct sound arguments of one's own and to evaluate the ...

There has been much debate in philosophy about the relation between identity and distinctness on the one hand, and various forms of discernibility on the other. For instance, philosophers have debated the truth of the Principle of the Identity of Indiscernibles (PII), which is naturally formulated using a second-order quantifier ranging over some class of properties of particular philosophical significance.

Meaning and Argument shifts introductory logic from the traditional emphasis on proofs to the symbolization of arguments. Another distinctive feature of this book is that it shows how the need for expressive power and for drawing distinctions forces formal language development. This revised edition includes expanded sections, additional exercises, and an updated bibliography. Updated and revised edition includes extended sections, additional exercises, and an updated bibliography. Distinctive approach in that this text is a philosophical, rather than mathematical introduction to logic. (...) Concentrates on symbolization and does all the technical logic simply with truth tables and no derivations at all. Contains numerous exercises and a corresponding answer key. Extensive appendix which allows the reader to explore subjects that go beyond what is usually covered in an introductory logic course. Features accompanying website at www.meaningargument.com. (shrink)

Thus far the logic out of which mathematics has developed has been First-order Predicate Calculus with Identity, that is the logic of the sentential functors, ¬, →, ∧, ∨, etc., together with identity and the existential and universal quotifiers restricted to quotify- ing only over individuals, and not anything else, such as qualities or quotities themselves. Some philosophers—among them Quine— have held that this, First-order Logic, as it is often called, con- stitutes the whole of logic. But that is a (...) mistake. It leaves out Second-order Logic, which we need if we are to characterize the natural numbers precisely, and pays scant attention to the logic of relations, especially transitive relations, which is the key to much of modern mathematics. Quine’s argument for restricting logic to First-order Logice was based on the grounds that only First- order logical theories display “Law and Order” and himself regards modal logic as belonging with witchcraft and superstition.1 Pred- icates are ontologically more suspect than individuals, and have a different logic, which is liable to give rise to paradox and inconsis- tency. Moreover, Second-order Logic lacks the completeness that First-order Logice has, which provides a pleasing parallel between syntactic and semantic notions, and argues for the analyticity of deductive logic. (shrink)

Call an argument a ‘happy sorites’ if it is a sorites argument with true premises and a false conclusion. It is a striking fact that although most philosophers working on the sorites paradox find it at prima facie highly compelling that the premises of the sorites paradox are true and its conclusion false, few (if any) of the standard theories on the issue ultimately allow for happy sorites arguments. There is one philosophical view, however, that appears to allow for at (...) least some happy sorites arguments: strict finitism in the philosophy of mathematics. My aim in this paper is to explore to what extent this appearance is accurate. As we shall see, this question is far from trivial. In particular, I will discuss two arguments that threaten to show that strict finitism cannot consistently accept happy sorites arguments, but I will argue that (given reasonable assumptions on strict finitistic logic) these arguments can ultimately be avoided, and the view can indeed allow for happy sorites arguments. (shrink)

Some students in the humanities take fright when introduced to the formal manipulations characteristic of elementary sentential & predicate logic. One way to lessen the pain of initiation is to start with word games, of which Lewis Carroll’s Doublets (section 1) is a familiar example. The paper presents some other games that successively introduce more of the..

This text is a short introduction to logic that was primarily used for accompanying an introductory course in Logic for Linguists held at the New University of Lisbon (UNL) in fall 2010. The main idea of this course was to give students the formal background and skills in order to later assess literature in logic, semantics, and related fields and perhaps even use logic on their own for the purpose of doing truth-conditional semantics. This course in logic does not replace (...) a proper introduction to semantics and is not intended as such, although parts of Chapter 1 and 4 could be used to supplement an introductory course in semantics. In contrast to other introductions it has a certain focus on ‘writing things down correctly.’ Proofs of metatheorems are omitted, though. -/- This is work in progress. Please send suggestions and corrigenda to erich@snafu.de. Have fun! (shrink)

This paper is a critical exposition of Prior’s theory of truth as expressed by the following truth locutions: (1) ‘it is true that’ prefixed to sentences; (2) ‘true proposition’; (3) true belief’, ‘true assertion’, ‘true statement’, etc.; (4) ‘true sentence’.

This paper replies to points Williams makes to his reply to Sayward’s criticism of Williams’s proposal of ‘for some p ___ states that p & p’ as an analysis of ‘___ is true’.

C. J. F, Williams proposed ‘for some p ___ states that p & p’ as a satisfactory analysis of ‘___ is true’. This paper takes issue with this claim.

This book introduces the notions and methods of formal logic from a computer science standpoint, covering propositional logic, predicate logic, and foundations ...

Formal logic provides us with a powerful set of techniques for criticizing some arguments and showing others to be valid. These techniques are relevant to all of us with an interest in being skilful and accurate reasoners. In this highly accessible book, Peter Smith presents a guide to the fundamental aims and basic elements of formal logic. He introduces the reader to the languages of propositional and predicate logic, and then develops formal systems for evaluating arguments translated into these languages, (...) concentrating on the easily comprehensible 'tree' method. His discussion is richly illustrated with worked examples and exercises. A distinctive feature is that, alongside the formal work, there is illuminating philosophical commentary. This book will make an ideal text for a first logic course, and will provide a firm basis for further work in formal and philosophical logic. (shrink)

Coherent, well organized text familiarizes readers with complete theory of logical inference and its applications to math and the empirical sciences. Part I deals with formal principles of inference and definition; Part II explores elementary intuitive set theory, with separate chapters on sets, relations, and functions. Last section introduces numerous examples of axiomatically formulated theories in both discussion and exercises. Ideal for undergraduates; no background in math or philosophy required.

Logic brings elementary logic out of the academic darkness into the light of day. Paul Tomassi makes logic fully accessible for anyone trying to come to grips with the complexities of this challenging subject. This book is written in a patient and user-friendly way which makes both the nature and value of formal logic crystal clear. This textbook proceeds from a frank, informal introduction to fundamental logical notions to a system of formal logic rooted in the best of our natural (...) deductive reasoning in daily life. The book includes plenty of exercise to put the students' reading to test, summay boxes of key points, a glossary and many illustrations. This book will be useful to any student who needs a patient and comprehensible introduction to what otherwise can be a daunting subject. (shrink)

In the Begriffschrift Frege drew no distinction—or anyway signalled no importance to the distinction—between quantifying into positions occupied by what he called eigennamen—singular terms—in a sentence and quantification into predicate position or, more generally, quantification into open sentences—into what remains of a sentence when one or more occurrences of singular terms are removed. He seems to have conceived of both alike as perfectly legitimate forms of generalisation, each properly belonging to logic. More accurately: he seems to have conceived of quantification (...) as such as an operation of pure logic, and in effect to have drawn no distinction between first-order, second-order and higherorder quantification in general. (shrink)