Alfred Tarski

A.1. Some philosophers, including Tarski and Russell, have concluded from a study of various versions of the Liar Paradox ‘that there must be a hierarchy of languages, and that the words “true” and “false”, as applied to statements in any given language, are themselves words belonging to a language of higher order’. In his famous essay on truth Tarski claimed that ‘colloquial’ language is inconsistent as a result of its property of ‘universality’: that is, whatever can be said at all (...) can in principle be said in it, with an extended vocabularly if necessary. Thus, in English we can talk about English expressions, what they denote, what they say, whether what they say is true or false, and so on: English contains its own metalanguage. This universality enables us to construct sentences which say of themselves that they are false, and by applying the law of excluded middle to them we easily derive a contradiction. Tarski concludes that ‘these antinomies seem to provide a proof that every language which is universal in the above sense, and for which the normal laws of logic hold, must be inconsistent’ . He then proposes to avoid such contradictions by the use of a hierarchy of languages such that statements about any one language can be made only in a different language at a higher level. (shrink)

This paper is an historical study of Tarski's methodology of deductive sciences (in which a logic S is identified with an operator Cn S , called the consequence operator, on a given set of expressions), from its appearance in 1930 to the end of the 1970s, focusing on the work done in the field by Roberto Magari, Piero Mangani and by some of their pupils between 1965 and 1974, and comparing it with the results achieved by Tarski and the Polish (...) school (?o?, Suszko, S?upecki, Pogorzelski, Wójcicki). In the last section of the paper we will then compare these works with some recent developments in algebraic logic: this will lead to a better understanding of the results of the methodology of deductive science, but at the same time will show some intrinsic limits to such an approach to logic. Even if Magari's work on diagonizable algebras and universal algebra and Mangani's axiomatization of MV-algebras and results in model theory are rather famous, the articles on closure operators, published in the 1960s, are almost totally unknown outside Italy (mainly because of a linguistic limitation, the papers we analyse having been written and published in Italian). This paper aims to fill the gap in the literature and to enable the international community to get acquainted with this part of Italian logic. The same applies to some works published in Barcelona (in Catalan) at the end of the 1970s, analysed in the last section. (shrink)

All arithmetical identities involving 1, addition, multiplication and exponentiation will be true in a 2-element model of Tarski's system if a certain sequence of natural numbers is not bounded. That sequence can be bounded only if the set of Fermat's prime numbers is finite.

All arithmetical identities involving 1, addition, multiplication and exponentiation will be true in a 2-element model of Tarski's system if a certain sequence of natural numbers is not bounded. That sequence can be bounded only if the set of Fermat's prime numbers is finite.

Tarski’s pioneering work on truth has been thought by some to motivate a robust, correspondence-style theory of truth, and by others to motivate a deflationary attitude toward truth. I argue that Tarski’s work suggests neither; if it motivates any contemporary theory of truth, it motivates conceptual primitivism, the view that truth is a fundamental, indefinable concept. After outlining conceptual primitivism and Tarski’s theory of truth, I show how the two approaches to truth share much in common. While Tarski does not (...) explicitly accept primitivism, the view is open to him, and fits better with his formal work on truth than do correspondence or deflationary theories. Primitivists, in turn, may rely on Tarski’s insights in motivating their own perspective on truth. I conclude by showing how viewing Tarski through the primitivist lens provides a fresh response to some familiar charges from Putnam and Etchemendy. (shrink)

Jamin Asay's book offers a fresh and daring perspective on the age-old question 'What is truth?', with a comprehensive articulation and defence of primitivism, the view that truth is a fundamental and indefinable concept. Often associated with Frege and the early Russell and Moore, primitivism has been largely absent from the larger conversation surrounding the nature of truth. Asay defends primitivism by drawing on a range of arguments from metaphysics, philosophy of language and philosophy of logic, and navigates between correspondence (...) theory and deflationism by reviving analytic philosophy's first theory of truth. In its exploration of the role that truth plays in our cognitive and linguistic lives, The Primitivist Theory of Truth offers an account of not just the nature of truth, but the foundational role that truth plays in our conceptual scheme. It will be valuable for students and scholars of philosophy of language and of metaphysics. (shrink)

The aim of this paper is to investigate whether Tarski’s truth definition explains the notion of truth as correspondence with reality and whether it is really a semantic definition of truth. I defend the view that, although Tarski succeeded in the task of constructing correct and adequate definitions, according to his own criteria of correctness and adequateness, the definitions obtained by his method neither are explanations of the main point of a correspondence theory of truth, the relationship between language and (...) reality on which depends the truth of a sentence, nor can be considered genuinely semantic. (shrink)

It is argued that the blind ascriptive role for the word true, its use, that is, in conjunction with descriptions of classes of sentences or with proper names of sentences (but not quote-names), is one which applies indiscriminately to sentences regardless of whether these are in languages we speak, can understand, or can translate into sentences that we do speak (and understand). Formal analogues of the ordinary word true as they arise in Tarskis seminal work, and in others, cannot replicate (...) this essential role of the ordinary word true. (shrink)

In his 1936 paper, "The Concept of Logical Consequence," Alfred Tarski set out the first formulation of the model-theoretic definition of logical consequence. This definition has hence become a central canon of contemporary logical inquiry. However, it has come under recent attack. In this dissertation, I present a defense of the standard model-theoretic analyses of the concepts of validity and consequence against various objections. ;In the first chapter, it is argued that the model-theoretic analysis of natural language argumentation is based (...) on determining relationships between structural properties of mathematical models and those of the language under study. This use of model theoretic structures involves the application of mathematical models to the description of a natural language; and as such, the determination of the analysis can best be decided in the context of discussing the analysis, qua mathematical analysis. ;In the second chapter, I discuss the distinction between representational semantics and interpretational semantics. I argue that Etchemendy presents us with a false dilemma: the semantics underlying the model-theoretic analyses of the logical properties is neither a representational semantics, nor an interpretational semantics. I then formulate a precise and defensible version of Tarski's Thesis. ;In chapter 3, I take up the two main lines of argument directed against Tarski's Thesis. First, I argue that neither Etchemendy's under-generational and over-generational examples, nor McGee's reliability problem argue against the formulation of Tarski's Thesis given in this work. Second, I argue that the claims brought out in Etchemendy's discussion of the Reduction Principle and in McGee's discussion of the Contingency Problem are mistaken, and that the conclusions they draw from these claims are unwarranted. ;Finally, chapter 4 takes up historical issues surrounding both the discrepancies between Tarski's original formulation of the model-theoretic definitions and their present day incarnations, and Etchemendy's attribution to Tarski of "Tarski's Fallacy." I argue that the historical account given Tarski's 1936 paper by Etchemendy is mistaken, and that only the most narrow and unkind reading supports the fallacy attribution. (shrink)

_Tarski’s World_ is an innovative and exciting method of introducing students to the language of first-order logic. Using the courseware package, students quickly master the meanings of connectives and qualifiers and soon become fluent in the symbolic language at the core of modern logic. The program allows students to build three-dimensional worlds and then describe them in first-order logic. The program, compatible with Macintosh and PC formats, also contains a unique and effective corrective tool in the form of a game, (...) which methodically leads students back through their errors if they wrongly evaluate the sentences in the constructed worlds. A brand new feature in this revised and expanded edition is student access to Grade Grinder, an innovative Internet-based grading service that provides accurate and timely feedback to students whenever they need it. Students can submit solutions for the program’s more than 100 exercises to the Grade Grinder for assessment, and the results are returned quickly to the students and optionally to the teacher as well. A web-based interface also allows instructors to manage assignments and grades for their classes. Intended as a supplement to a standard logic text, _Tarski’s World_ is an essential tool for helping students learn the language of logic. (shrink)

Many of Tarski’s better known papers are either about or include lengthy discussions of how to properly define various concepts: truth, logical consequence, semantic concepts, or definability. In general, these papers identify two primary conditions for successful definitions: formal correctness and material adequacy. Material adequacy requires that the concept expressed by the formal definition capture the intuitive content of truth. Our primary interest in this paper is to better understand Tarski’s thinking about material adequacy, and whether components of his view (...) developed over time. More precisely, we are concerned with how Tarski’s understanding of the content of the common-sense, every-day usage of truth may have developed over time. We distinguish this concern from the character of the extensional criterion of adequacy Tarski proposes: that a materially adequate definition must entail all instances of Convention T. We will develop our reading of Tarski as follows: first, we will review the “Polemical Remarks,” focusing primarily on §§14 and 17, and Tarski’s references to Naess’ empirical research. Next, we will provide a summary and discussion of Naess’ work, especially his findings with respect to Tarski’s definition of truth and his research that suggests there is no single common or everyday concept of truth. Third, we will consider several possible objections to our interpretation of the Tarski–Naess dialectic. We will conclude that Tarski’s conception of material adequacy developed over time, potentially because of what he had learned through his interactions with Naess. (shrink)

Philosophical theorizing about truth manifests a desire to conform to the ordinary or folk notion of truth. This practice often involves attempts to accommodate some form of correspondence. We discuss this accommodation project in light of two empirical projects intended to describe the content of the ordinary conception of truth. One, due to Arne Naess, claims that the ordinary conception of truth is not correspondence. Our more recent study is consistent with Naess’ result. Our findings suggest that contextual factors and (...) respondent gender affect whether the folk accept that correspondence is sufficient for truth. These findings seem to show that the project of accommodating the ordinary notion of truth is more difficult than philosophers had anticipated because it is fragmentary. (shrink)

John Etchemendy (1990) has argued that Tarski's definition of logical consequence fails as an adequate philosophical analysis. Since then, Greg Ray (1996) has defended Tarski's analysis against Etchemendy's criticisms. Here, I'll argue that--even given Ray's defense of Tarski's definition--we may nevertheless lay claim to the conditional conclusion that 'if' Tarski intended a conceptual analysis of logical consequence, 'then' it fails as such. Secondly, I'll give some reasons to think that Tarski 'did' intend a conceptual analysis of logical consequence.

This paper concerns Tarski’s use of the term “model” in his 1936 paper “On the Concept of Logical Consequence.” Against several of Tarski’s recent defenders, I argue that Tarski employed a non-standard conception of models in that paper. Against Tarski’s detractors, I argue that this non-standard conception is more philosophically plausible than it may appear. Finally, I make a few comments concerning the traditionally puzzling case of Tarski’s ω-rule example.

We try to explain Tarski's conception of logical notions, as it emerges from alecture of his, delivered in 1966 and published posthumously in 1986 (Historyand Philosophy of Logic 7, 143–154), a conception based on the idea ofinvariance. The evaluation of Tarski's proposal leads us to consider an interesting(and neglected) reply to Skolem in which Tarski hints at his own point of view onthe foundations of set theory. Then, comparing the lecture of 1966 with Tarski'slast work and with an earlier paper (...) written with Lindenbaum, it is shown thatTarski's conception of logical notions, with its essentially type-theoretic character,did not undergo any significant modifications throughout his life. A remark onTarski's prudential attitude on the topic in the famous paper on the concept oflogical consequence (and elsewhere) concludes our paper. (shrink)

This paper is a contribution to the reconstruction of Tarski’s semantic background in the light of the ideas of his master, Stanislaw Lesniewski. Although in his 1933 monograph Tarski credits Lesniewski with crucial negative results on the semantics of natural language, the conceptual relationship between the two logicians has never been investigated in a thorough manner. This paper shows that it was not Tarski, but Lesniewski who first avowed the impossibility of giving a satisfactory theory of truth for ordinary language, (...) and the necessity of sanitation of the latter for scientific purposes. In an early article (1913) Lesniewski gave an interesting solution to the Liar Paradox, which, although different from Tarski’s in detail, is nevertheless important to Tarski’s semantic background. To illustrate this I give an analysis of Lesniewski’s solution and of some related aspects of Lesniewski’s later thought. (shrink)

In ‘The Trouble with Tarski’, The Philosophical Quarterly, 48 (1998), pp. 1–22, Jonathan Harrison attacks ‘Tarski‐style’ truth theories for both formalized and natural languages, on the grounds that (1) truth cannot be a property of sentences; (2) if it could be, T‐sentences would have to be necessary truths, which they are not; and (3) T‐sentences are not necessarily true and can even can be false. I reply that (1) cannot be an objection to Tarskian truth theories, since these can be (...) formulated in terms of whatever truth bearers might be. Thesis (2) is unjustified: Harrison's argument for it depends on an equivocation. Thesis (3) is false, since the right‐hand side of a T‐sentence is a meta‐language translation of the object‐language sentence described on the left‐hand side, and this guarantees its truth. (shrink)

A revision of a sermon on the evils of calling model theory “semantics”, preached at Notre Dame on Saint Patrick’s Day, 2005. Provisional version: references remain to be added. To appear in Mathematics, Modality, and Models: Selected Philosophical Papers, coming from Cambridge University Press.

Theories of linguistic meaning have been a major influence in twentieth century philosophy. This is due, in part, to the assumption that meaning is the crucial and interesting thing about language. To know the meaning of an expression is to understand it, and since understanding is central to philosophy in many different ways, it should be no surprise that the notion of meaning has often taken center stage. The aim of this paper is to briefly explore some influential views concerning (...) linguistic meaning. The final objective will be to demonstrate some alternatives which are open to theory with respect to this notion,for there are those who have wanted to ban talk of meaning from serious scientific discourse. The point is that many of the disadvantages of traditional notions of meaning are avoidable¾in particular, they are avoidable along a path which starts from Frege and moves on via Tarski and Davidson. (shrink)

We introduce a notion of semantical closure for theories by formalizing Nepeivoda notion of truth. [10]. Tarski theorem on truth definitions is discussed in the light of Kleene's three valued logic (here treated with a formal reinterpretation of logical constants). Connections with Definability Theory are also established.

The work on set theory made by A. Tarski in the years 1924-1950 is very interesting, but little know.We develope partial questions in set theory in the moment that A. Tarski intervenes and his contributionsand also influences.The principals aims in this development are:1. The axiom of choice [A.C.] and his equivalents;2. the general continuum hypothesis [G.C.H.] and the A.C.;3. the dual trichotomy principle;4. the inaccessible cardinals and his relation with the A.C. and the G.C.H.;5. the notion of finite set and (...) his relation with the A.C and the G.C.H.;6. the almost disjoint set and their relation with the G.C.H.;and finally,7. the results in Berkeley. (shrink)

This paper describes Tarski’s project of rehabilitating the notion of truth, previously considered dubious by many philosophers. The project was realized by providing a formal truth definition, which does not employ any problematic concept.

J.C. Beall and Greg Restall's Generalised Tarski Thesis is a generalisation of the seemingly diverse conceptions of logical consequence. However, even their apparently general account of consequence makes necessary truth-preservation a necessary condition. Sentences in the imperative mood pose a problem for any truth-preservationist account of consequence, because imperatives are not truth-apt but seem to be capable of standing in the relation of logical consequence. In this paper, I show that an imperative logic can be formulated that solves the problem (...) of imperative consequence by leading naturally to a further generalisation of the GTT. (shrink)

Down through the ages, logic has adopted many strange and awkward technical terms: assertoric, prove, proof, model, constant, variable, particular, major, minor, and so on. But truth-value is a not a typical example. Every proposition, even if false, no matter how worthless, has a truth-value:even “one plus two equals four” and “one is not one”. In fact, every two false propositions have the same truth-value—no matter how different they might be, even if one is self-contradictory and one is consistent. It (...) is not such a big surprise that every true proposition, no matter how worthless, has a truth-value. Every proposition, whether valuable or worthless, has a truth-value.But it is a little strange that every two true propositions, no matter how different they might be, have the same truth-value. The Pythagorean Theorem has the same truth-value as the proposition that one is one. It is a stretch to think of truth-values as values in any of the normal senses of the word ‘value’. (shrink)

Alfred Tarski (1901--1983) is widely regarded as one of the two giants of twentieth-century logic and also as one of the four greatest logicians of all time (Aristotle, Frege and Gödel being the other three). Of the four, Tarski was the most prolific as a logician. The four volumes of his collected papers, which exclude most of his 19 monographs, span over 2500 pages. Aristotle's writings are comparable in volume, but most of the Aristotelian corpus is not about logic, whereas (...) virtually everything written by Tarski concerns logic more or less directly. There is no doubt that Tarski wrote more on logic than any other author; he started publishing on logic in 1921 at the age of 20 and continued until his death at the age of 82. Two of his works appeared posthumously [Hist. Philos. Logic 7 (1986), no. 2, 143--154; MR0868748 (88b:03010); Tarski and Givant, A formalization of set theory without variables, Amer. Math. Soc., Providence, RI, 1987; MR0920815 (89g:03012)]. Tarski's voluminous writings were widely scattered in numerous journals, some quite rare. It has been extremely difficult to study the development of Tarski's thought and to trace the interconnections and interdependence of his various papers. Thanks to the present collection all this has changed, and it is likely that the increased accessibility of Tarski's papers will have the effect of increasing Tarski's already enormous influence. (shrink)

In this manuscript, published here for the first time, Tarski explores the concept of logical notion. He draws on Klein's Erlanger Programm to locate the logical notions of ordinary geometry as those invariant under all transformations of space. Generalizing, he explicates the concept of logical notion of an arbitrary discipline.

Tarski defined a way of assigning to each Boolean algebra, B, an invariant inv(B) ∈ In, where In is a set of triples from ℕ, such that two Boolean algebras have the same invariant if and only if they are elementarily equivalent. Moreover, given the invariant of a Boolean algebra, there is a computable procedure that decides its elementary theory. If we restrict our attention to dense Boolean algebras, these invariants determine the algebra up to isomorphism. In this paper we (...) analyze the complexity of the question "Does B have invariant x?" For each x ∈ In we define a complexity class Γx that could be either Σⁿ, Πⁿ, Σⁿ ∧ Πⁿ, or Πω+1 depending on x, and we prove that the set of indices for computable Boolean algebras with invariant x is complete for the class Γx. Analogs of many of these results for computably enumerable Boolean algebras were proven in earlier works by Selivanov. In a more recent work, he showed that similar methods can be used to obtain the results for computable ones. Our methods are quite different and give new results as well. As the algebras we construct to witness hardness are all dense, we establish new similar results for the complexity of various isomorphism problems for dense Boolean algebras. (shrink)

The aim of the article is to outline the historical background and the present state of the methodology of deductive systems invented by Alfred Tarski in the thirties. Key notions of Tarski's methodology are presented and discussed through, the recent development of the original concepts and ideas.

It is well known that Tarski proved a result which can be stated roughly as: no sufficiently rich, consistent, classical language can contain its own truth definition. Tarski's way around this problem is to deal with two languages at a time, an object language for which we are defining truth and a metalanguage in which the definition occurs. An obvious question then is: under what conditions can we construct a definition of truth for a given object language. Tarski claims that (...) it is necessary and sufficient that the metalanguage be "essentially richer". Our contention, put bluntly, is that this claim deserves more scrutiny from philosophers than it usually gets and in fact is false unless "essentially richer" means nothing else than "sufficient to contain a truth definition for the object language.". (shrink)

In his classic 1936 paper Tarski sought to motivate his definition of logical consequence by appeal to the inference form: P(0), P(1), . . ., P(n), . . . therefore ∀nP(n). This is prima facie puzzling because these inferences are seemingly first-order and Tarski knew that Gödel had shown first-order proof methods to be complete, and because ∀nP(n) is not a logical consequence of P(0), P(1), . . ., P(n), . . . by Taski's proposed definition. An attempt to resolve (...) the puzzle due to Etchemendy is considered and rejected. A second attempt due to Gómez-Torrente is accepted as far as it goes, but it is argued that it raises a further puzzle of its own: it takes the plausibility of Tarski's claim that his definition captures our common concept of logical consequence to depend upon our common concept being a reductive conception. A further interpretation of what Tarski had in mind when he offered the example is proposed, using materials well known to Tarski at the time. It is argued that this interpretation makes the motivating example independent of reductive definitions which take natural numbers to be higher-order set theoretic entities, and it also explains why he did not regard the distinction between defined and primitive terms as pressing, as was the distinction between logical and nonlogical terms. (shrink)

In his 1936 article, "Uber den Begriff der logischen Folgerung," Tarski claims to have provided precise definitions of the concepts of logical truth and logical consequence that remain "close in essentials" to the "common" or "everyday" concepts. In this dissertation, I examine Tarski's account of these notions, as well as the standard model theoretic definitions that are based on that analysis. I argue that Tarski's analysis, and hence in turn its model theoretic heirs, are fundamentally mistaken, that they do not (...) capture the essential features of our ordinary understanding of those notions. I claim that the account's misdirection is, in a sense, quite obvious, but that it has been disguised in various different ways. First is a fallacious argument that seems to have been offered by Tarski in support of his analysis, second is the conflation of the model theoretic definitions with what I call "representational semantics," and third is a confusion of the principle underlying Tarski's account with a completely uncontroversial principle concerning the closure of logical truth under logical consequence. (shrink)

The following is the text of an invited lecture for the LICS 2005 meeting held in Chicago June 26-29, 2005.1 Except for the addition of references, footnotes, corrections of a few points and stylistic changes, the text is essentially as delivered. Subsequent to the lecture I received interesting comments from several colleagues that would have led me to expand on some of the topics as well as the list of references, had I had the time to do so.