Frege, Friedrich Ludwig Gottlob
FREGE, FRIEDRICH LUDWIG GOTTLOB
(b. Wismar, Germany, 8 November 1848; d. Bad Kleinen, Germany, 26 July 1925),
mathematics, logic, foundations of mathematics. For the original article on Frege see DSB, vol. 5.
Although a mathematician, Gottlob Frege is regarded as one of the founding fathers of modern (analytical) philosophy. With his Begriffsschrift (concept script) of 1879 he created modern mathematical logic. He used it as a linguistic tool for a program of founding mathematical concepts exclusively on logical concepts (logicism). Frege was involved in controversies with representatives of the algebraic tradition in logic concerning the power of the different systems of symbolic logic, and with David Hilbert on the nature of mathematical axiom systems.
Frege in Jena . Frege spent most of his academic life at the University of Jena, except for five semesters of studies in Göttingen (1871–1873). He took courses in mathematics, physics, chemistry, and philosophy. Among his most important teachers in Jena were Karl Snell, who followed Jakob Friedrich Fries as chair of mathematics and physics, and Ernst Carl Abbe, at that time privatdozent for mathematics. Abbe became Frege’s mentor. He encouraged Frege to transfer to Göttingen in order to complete his university studies and later supported him in his career.
Back in Jena, Frege applied for the post of a privatdozent for mathematics, submitting as Habilitationsschrift“Methods of Calculation Based on an Extension of the Concept of Quality,” which contributed to the theory of functional equations, in particular iteration theory. Abbe initiated Frege’s promotion to außerordentlicher Professor (roughly equivalent to associate professor or reader) of mathematics in 1879. This early promotion was possible because Frege had published his first monograph, Begriffsschrift, in January of that year. In 1866 Abbe had become a scientific consultant for improving the construction of microscopes built by the Carl Zeiss optics industry. In 1875 he became an associate and limited partner of Zeiss. Abbe set up the Carl Zeiss Foundation (1889) by first establishing a fund for scientific purposes (Ministerialfond für wissenschaftliche Zwecke) in 1886, supporting teaching and research in mathematics and sciences at the University of Jena. Abbe’s foundation also made an improvement in Frege’s remuneration possible, and later financially supported his promotion to ordentlicher Honararprofessor (a payroll professorship in honor of the person) in 1896.
In 1907 Frege was awarded the prestigious title of Hofrat. His growing reputation is indicated by Ludwig Wittgenstein’s visit in 1911 (further visits took place in 1912 and 1913). In summer semester 1913 Rudolf Carnap attended Frege’s course Begriffsschrift II, and another course, Logic in Mathematics, in 1914. In 1918 Frege retired after having been on sick leave for a year. He moved to Bad Kleinen, a resort near Wismar. On the initiative of Heinrich Scholz, Frege’s Nachlass (literary estate) was transferred in 1935 to Münster, where it was purportedly destroyed during a bomb raid on Münster on 25 March 1945.
Logic . Frege’s publication of the Begriffsschrift is regarded in the early twentyfirst century as “the single most important event in the development of modern logic” (Thiel and Beaney, p. 26). In this work, Frege created the first strict logical calculus in the modern sense, based on precise definitions of expressions and deduction rules arriving for the first time at an axiomatic development of classical quantification theory. Frege replaced the traditional analysis of elementary statements into subject and predicate with an analysis of a proposition into function and argument, which could be used to express the generality of a statement (and with this also existence statements) by bound variables and quantifiers.
It can be assumed that Frege took over the term Begriffsschrift from Friedrich Adolf Trendelenburg’s characterization of Gottfried Wilhelm Leibniz’s general characteristics (1854). The term had, however, already been used by Wilhelm von Humboldt in a treatise (1824) on the letter script and its influence on the construction of language.
In a lengthy review of the Begriffsschrift (1880), Ernst Schröder accused Frege of ignoring George Boole’s algebra of logic, first presented in The Mathematical Analysis of Logic (1847). Frege answered in articles (published only posthumously) by comparing Boole’s calculatory logic with his own, where he determined quantification theory as the main point of deviation (Frege, 1880–1881, 1882). It is indeed historically true that the Booleans had no quantification theory at that time, but this cannot be regarded as an essential difference between these variations of symbolic logic on a systematic level, because in 1883 the U.S. logician Charles S. Peirce and his student Oscar Howard Mitchell developed an almost equivalent quantification theory within the algebra of logic. The essential difference between the algebra of logic and Frege’s mathematical logic can thus be seen in different interpretations of the judgment. Another essential difference can be seen in the fact that Frege aimed at giving a logical structure of judgeable contents, which implied an inherent semantics. The Booleans, in contrast, were interested in logical structures themselves, which could be applied in different domains. Their systems allowed various interpretations. This required a supplementary external semantics.
Logicism . Frege’s work was above all devoted to investigations on the nature of number. It was, thus, essentially philosophical. There is evidence that he was influenced by the philosophy of his contemporaries, especially by neoKantian approaches. These influences found their way into Frege’s philosophy of mathematics with its metaphysical qualities.
Contrary to Immanuel Kant, who regarded mathematical (arithmetical and geometrical) propositions as examples for synthetic a priori propositions, that is, propositions that are not empirical, but enlarging knowledge, Frege wanted to prove that arithmetic could completely be founded on logic, that is, that each arithmetical concept, in particular the concept of number, could be derived from logical concepts. Arithmetic was, thus, analytical.
The logicist program is only sketched in the Begriffsschrift, where Frege gave purely logical definitions of equinumerousity and the successor relation. In his next book, the Grundlagen der Arithmetik (1884). Frege formulated the classical logicistic definition of number, according to which the number n is defined as the extension of the concept “equinumerous to the concept F_{n}” with F_{n}standing for a concept with exactly n objects falling under it. The series of F_{n}s starts with F_{0} = ¬x = x. F_{n+1}can be reconstructed recursively from F_{n}. The number 0 is defined as the extension of the concept “equinumerous to the concept ‘different from itself,’” and the number 1 as the extension of the concept “equinumerous to the concept ‘equals 0.’” The purely logical foundation of mathematics should not only disprove the Kantian paradigm, but also refute empiricist approaches to mathematics such as the one advocated by John Stuart Mill, and with this psychological interpretations of numbers as mental constructions. Frege pointedly expressed this criticism of psychologism in his harsh review of Edmund Husserl’s Philosophie der Arithmetik in 1894, as a result of which Husserl was brought to revise the foundational program of phenomenology and convert to antipsychologism.
Frege elaborated the logicistic program in the two volumes of the Grundgesetze der Arithmetik (1893/1903). In this last of his monographs Frege also presented the mature version of his ontology, developed earlier in the three papers “Function and Concept” (1891), “On Sinn und Bedeutung” (1892), and “Concept and Object” (1892), all three currently regarded as classic texts of analytical philosophy. There he further elaborated his earlier distinction between concept and object. In particular he introduced in the Grundgesetze valueranges considered as a special kind of objects. The identity criterion is given in Basic Law V, according to which the valueranges of two functions are identical if the functions coincide in their values for every argument, with this giving the modern abstraction schema. In terms of concepts the law says that whatever falls under the concept F falls under the concept G and vice versa, if and only if the concepts F and G have the same extension.
Frege’s conception of logicism failed, as Frege himself diagnosed, because of Basic Law V. Frege suggested an ad hoc solution forbidding that the extension of a concept may fall under the concept itself. This solution was proved to be insufficient by Stanis≠aw LeŚniewski (1939, unpublished) and Willard Van Orman Quine in 1955, but it indicates that the logical form of Basic Law V may be innocent of the emergence of the paradox and that the formation rules for function names may be too liberal in allowing impredicative function names.
In his latest publications Frege gave up logicism. He abandoned the talk of extensions of concepts and valueranges, and the idea of numbers as logical objects, although he still held that they are objects of some other kind, based on the source of “geometrische Erkenntnisquelle,” that is, pure intuition.
Frege’s logicist program was later revived by the proponents of Fregearithmetic and neologicism. In some of these directions Basic Law V is replaced by Hume’s principle, according to which two concepts F and G have the same number if and only if they are equinumerous, that is, if there is a onetoone correspondence between the F’s and G's.
The Nature of Axiomatics . After the failure of his logicistic program, Frege focused his research on geometry as the foundational discipline of mathematics. He kept the traditional understanding of geometry as an intuitive discipline, thereby opposing David Hilbert’s new formalistic approach to geometry that came along with a new kind of axiomatics. Frege’s opposition had its prehistory in his criticism of the older arithmetical formalism presented in a paper “Über formale Theorien der Arithmetik” (1885), taken up again in papers against his Jena colleague in mathematics, Carl Johannes Thomae (1906/1908). In these papers Frege opposes the understanding of arithmetic as a purely formal game with calculations bare of any contents. The older formalism regards arithmetic as a game like chess. It starts from certain initial formulas, then derives new formulas using a fixed set of transformation rules. But, neither the initial formulas nor the transition rules are justified, so the derived formulas are not justified either. Therefore, Frege concludes, these approaches could not provide any contribution to the foundations of arithmetic.
Hilbert overcame the traditional conception of axiomatics according to the model of Euclid’s Elements by giving an example. In his Grundlagen der Geometrie of 1899 he gave an axiomatic presentation of Euclidean geometry. Hilbert’s system proceeds from “thought things” in the Kantian sense, products of the human mind, but empty concepts because of lacking any element of (empirical) intuition. The geometrical concepts were not directly defined, but implicitly gained as concepts obeying the features set by some group of axioms, and justified by proving the independence of the axioms from one another, the completeness of the system, and its consistency. The formalistic approach aims at a theory of structures. This is pointedly expressed in Hilbert’s letter to Frege of 29 December 1899, in which Hilbert claimed that every theory is only a halftimbering or schema of concepts and implications with arbitrary basic elements. If instead of the system of points some system love, law, chimney sweep is thought, and if all axioms are regarded as relations between these elements, then all theorems, for example Pythagoras’s theorem, would be valid for them.
In a letter sent two days earlier, Frege had correctly criticized Hilbert’s use of implicit definitions arguing that he had blurred the differences between axioms and definitions. It became clear that Frege stuck to the traditional (Aristotelian) understanding of axioms in geometry, calling axioms sentences that are true but not proved, because they have emerged from a source of knowledge completely different from the logical, a source that can be called spatial intuition. From the truth of the axioms follows that they do not contradict each other, so no consistency of proof was needed. Hilbert answered that if the arbitrarily set axioms do not contradict each other with all their implications, then they are true and the defined objects exist. For Hilbert consistency (logical possibility) is, thus, the criterion of truth and existence.
Hilbert rejected Frege’s suggestion to publish the exchange of letters, so Frege took up his criticism in a series of papers published in 1903 and 1906 on the foundations of geometry, where he argued for his antiformalistic position. He demanded that after having defined the concept “point,” it should be possible to determine whether a certain object, for example, his pocket watch, was a point or not.
The two controversies mentioned show that Frege followed that traditional understanding of philosophy as allembracing fundamental discipline that formed, along with logic, logical ontology, and epistemology the foundation for mathematics and sciences. He did not share the pragmatic attitude of some influential contemporaries in mathematics and sciences (like Hilbert) to keep philosophy away from their mathematical and scientific practice by simply fading out philosophical problems. Nevertheless, Frege opened the way for directions like philosophy of science, which aimed at bridging the gap between philosophy on the one hand and mathematics and science on the other, and which became successful in the twentieth century. His influence on Bertrand Russell’s logicism, codified in Principia Mathematica, Russell’s joint work with Alfred North Whitehead (1910/13), is well known. Through Carnap, Frege gained influence on logic and foundational research in the neopositivist movement of the Vienna Circle, which constituted the context of Kurt Gödel’s shaping of modern logic and foundational studies.
SUPPLEMENTARY BIBLIOGRAPHY
WORKS BY FREGE
“Methods of Calculation Based on an Extension of the Concept of Quantity” (1874). In McGuiness, Collected Papers on Mathematics, Logic, and Philosophy, 56–92.
Begriffsschrift, eine der arithmetischen nachgebildete Formelsprache des reinen Denkens. Halle, Germany: L. Nebert, 1879. In Conceptual Notation and Related Articles, translated and edited with a biography and introduction by Terence Ward Bynum, 101–203. Oxford: Oxford University Press, 1972.
“Boole’s Logical Calculus and the ConceptScript.” (1880–1881). In Hermes et al., Posthumous Writings, 9–46.
“Boole’s Logical FormulaLanguage and My ConceptScript.”(1882). In Hermes et al., Posthumous Writings, 47–52.
Die Grundlagen der Arithmetik, eine logisch mathematische Untersuchung über den Begriff der Zahl. Breslau, Germany: W. Koebner, 1884. Translated by John L. Austin as The Foundations of Arithmetic. 2nd ed. Oxford: Blackwell, 1953.
“On Formal Theories of Arithmetic” (1885). In McGuiness, Collected Papers on Mathematics, Logic, and Philosophy, 112–121.
“Function and Concept” (1891). In Beany, The Frege Reader, 130–148.
“On Sinn und Bedeutung” (1892). In Beany, The Frege Reader, 151–171.
“On Concept and Object.” (1892). In Beany, The Frege Reader, 181–193.
“Grundgesetze der Arithmetik.” 2 Vols. Jena: H. Pohle, 1893 (Vol. 1); 1903 (Vol. 2).
Review of E. H. Husserl, Philosophie der Arithmatik I. (1894). In McGuiness, Collected Papers on Mathematics, Logic, and Philosophy, 195–209.
“On the Foundations of Geometry. First Series.” (1903). In McGuiness, Collected Papers on Mathematics, Logic, and Philosophy, 273–284.
“On the Foundations of Geometry. Second Series.” (1906). In McGuiness, Collected Papers on Mathematics, Logic, and Philosophy, 293–340./bibcit.composed>
“Reply to Mr. Thomae’s Holiday Causerie.” (1906). In McGuiness, Collected Papers on Mathematics, Logic, and Philosophy, 341–345.
“Renewed Proof of the Impossiblity of Mr. Thomae’s Formal Arithmetic.” (1908). In McGuiness, Collected Papers on Mathematics, Logic, and Philosophy, 346–350.
Posthumous Writings. Edited by Hans Hermes, Friedrich Kambartel, and Friedrich Kaulbach, with the assistance of Gottfried Gabriel and Walburga Rödding. Translated by Peter Long and Roger White, with the assistance of Raymond Hargreaves. Chicago: University of Chicago Press, 1979.
Philosophical and Mathematical Correspondence. Edited by Gottfried Gabriel, et al. Abridged for the English edition by Brian McGuinness. Translated by Hans Kaal. Chicago: University of Chicago Press, 1980.
Collected Papers on Mathematics, Logic, and Philosophy. Edited by Brian McGuinness. Translated by Max Black et al. Oxford: Blackwell, 1984.
Kleine Schriften. 2nd ed. Edited by Ignacio Angelelli. Hildesheim, Germany: G. Olms, 1990. Collection of Frege’s published papers and reviews, together with some letters and notes on Frege’s works by H. Scholz and E. Husserl.
“Diary: Written by Professor Dr. Gottlob Frege in the Time from 10 March to 9 April 1924.” Edited by Gottfried Gabriel and Wolfgang Kienzler. Inquiry 39 (1996): 303–342.
The Frege Reader. Edited by Michael Beaney. Oxford: Blackwell, 1997. The volume brings together all of Frege’s seminal writings, substantial parts of his three books, and selections from his posthumous writings and correspondence.
Frege’s Lectures on Logic: Carnap’s Student Notes, 1910–1914. Translated and edited by Erich H. Reck and Steve Awodey. Chicago: Open Court, 2004. Gives evidence for Frege’s late positions in logic and foundations. With an introductory essay by Gottfried Gabriel and a paper by the editors on Frege’s influence on the development of logic.
OTHER SOURCES
Beaney, Michael. Frege: Making Sense. London: Duckworth, 1996. Frege’s concept of sense within his philosophy as a whole.
Beaney, Michael, and Erich H. Reck, eds. Gottlob Frege: Critical Assessments of Leading Philosophers. 4 vols. London: Routledge, 2005. Comprehensive collection of papers on Frege.
Brady, Geraldine. From Peirce to Skolem: A Neglected Chapter in the History of Logic. Amsterdam: Elsevier, 2000. Stresses the significance of the algebraic tradition for the development of logic.
Demopoulos, William, ed. Frege’s Philosophy of Mathematics. Cambridge, MA: Harvard University Press, 1995.
Dummett, Michael. Frege: Philosophy of Language. 2nd ed. London: Duckworth, 1981.
———. Frege and Other Philosophers. Oxford: Clarendon Press; 1991.
———. Frege: Philosophy of Mathematics. Cambridge, MA: Harvard University Press, 1991.
Gabriel, Gottfried, and Uwe Dathe, eds. Gottlob Frege: Werk und Wirkung; Mit den unveröffentlichten Vorschlägen für ein Wahlgesetz von Gottlob Frege. Paderborn, Germany: Mentis, 2000.
GrattanGuinness, Ivor. The Search for Mathematical Roots, 1870–1940: Logics, Set Theories, and the Foundations of Mathematics from Cantor through Russell to Gödel. Princeton, NJ: Princeton University Press, 2000. See pp. 177–199. Frege’s role within the development of research in logic and the foundations of mathematics.
Gronau, Detlef. “Gottlob Frege’s Beiträge zur Iterationstheorie und zur Theorie der Funktionalgleichungen.” In Gottlob Frege: Werk und Wirkung; Mit den unveröffentlichten Vorschlägen für ein Wahlgesetz von Gottlob Frege, edited by Gottfried Gabriel and Uwe Dathe, 151–169. Paderborn, Germany: Mentis, 2000.
Hale, Bob, and Crispin Wright. The Reason’s Proper Study: Essays towards a NeoFregean Philosophy of Mathematics. Oxford: Clarendon Press, 2001. Collection of papers neoFregeanism and Frege arithmetic.
Kreiser, Lothar. Gottlob Frege: Leben—Werk—Zeit. Hamburg, Germany: Meiner, 2001. Fullscale biography of Frege.
Newen, Albert, Ulrich Nortmann, and Rainer StuhlmannLaeisz, eds. Building on Frege: New Essays on Sense, Content, and Concept. Stanford, CA: CSLI Publications, 2001. Collection of essays on Frege’s significance and heritage.
Quine, Willard Van Orman. “On Frege’s Way Out.” Mind, n.s., 64 (1955): 145–159. Proof that Frege’s solution of Russell’s paradox was not feasible.
Schirn, Matthias, ed. Frege: Importance and Legacy. Berlin: de Gruyter, 1996. Collection of essays on Frege’s significance and heritage.
Schröder, Ernst. “Review of Frege, 1879.” Zeitschrift für Mathematik und Physik. Historischlitterarische Abteilung 25 (1880): 81–94.
Sluga, Hans D. Gottlob Frege. London: Routledge and Kegan Paul, 1980.
Sullivan, Peter M. “Frege’s Logic.” In Handbook of the History of Logic, vol. 3, edited by Dov M. Gabbay and John Woods, 659–750. Amsterdam: Elsevier North Holland, 2004.
Thiel, Christian. “Zur Inkonsistenz der Fregeschen Mengenlehre.” In Frege und die moderne Grundlagenforschung: Symposium, gehalten in Bad Homburg im Dezember 1973, edited by Christian Thiel, 134–159. Meisenheim am Glan, Germany: Verlag Anton Hain, 1975.
———. “‘Not Arbitrarily and Out of a Craze for Novelty’: The Begriffsschrift 1879 and 1893.’’ In Gottlob Frege: Critical Assessments of Leading Philosophers, 4 vols., edited by Michael Beaney and Erich H. Reck, vol. 2, 13–28. London: Routledge, 2005. Surveys the nature of Frege’s logical notation and its development.
Thiel, Christian, and Michael Beaney. “Frege’s Life and Work: Chronology and Bibliography.” In Gottlob Frege: Critical Assessments of Leading Philosophers, 4 vols., edited by Michael Beaney and Erich H. Reck, vol. 1, 23–39. London: Routledge, 2005. Brief chronology on the basis of information now available, and comprehensive bibliography.
Weiner, Joan. Frege Explained: From Arithmetic to Analytic Philosophy. Chicago: Open Court, 2004. Compact explanation of Frege’s work.
Volker Peckhaus
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Frege, Friedrich Ludwig Gottlob
Frege, Friedrich Ludwig Gottlob
(b. Wismar, Germany, 8 November 1848; d. Bad Kleinen, Germany, 26 July 1925)
logic, foundations of mathematics.
Gottlob Frege was a son of Alexander Frege, principal of a girl’s high school, and of Auguste Bialloblotzky. He attended the Gymnasium in Wismar, and from 1869 to 1871 he was a student at Jena. He then went to Göttingen and took courses in mathematics, physics, chemistry, and philosophy for five semesters. In 1873 Frege received his doctorate in philosophy at Göttingen with the thesis, Ueber eine geometrische Darstellung der imäginaren Gebilde in der Ebene. The following year at Jena he obtained the venia docendi in the Faculty of Philosophy with a dissertation entitled “Rechungsmethoden, die sich auf eine Erweitung des Grössenbegriffes gründen,” which concerns oneparameter groups of functions and was motivated by his intention to give such a definition of quantity as gives maximal extension to the applicability of the arithmetic based upon it. The idea presented in the dissertation of viewing the system of an operation f and its iterates as a system of quantities, which in the introduction to his Grundlagen der Arithmetik (1884) Frege essentially ascribes to Herbart, hints at the notion of f sequence expounded in his Begriffsschrift (1879).
After the publication of the Begriffsschrift, Frege was appointed extraordinary professor at Jena in 1879 and honorary professor in 1896. His stubborn work toward his goal—the logical foundation of arithmetic—resulted in his twovolume Grundgesetze der Arithmetik (1893–1903). Shortly before publication of the second volume Bertrand Russell pointed out in 1902, in a letter to Frege, that his system involved a contradiction. This observation by Russell destroyed Frege’s theory of arithmetic, and he saw no way out. Frege’s scientific activity in the period after 1903 cannot be compared with that before 1903 and was mainly in reaction to the new developments in mathematics and its foundations, especially to Hilbert’s axiomatics. In 1917 he retired. His Logische Untersuchungen, written in the period 1918–1923, is an extension of his earlier work.
In his attempt to give a satisfactory definition of number and a rigorous foundation to arithmetic, Frege found ordinary language insufficient. To overcome the difficulties involved, he devised his Begriffsschrift as a tool for analyzing and representing mathematical proofs completely and adequately. This tool has gradually developed into modern mathematical logic, of which Frege may justly be considered the creator.
The Begriffsschrift was intended to be a formula language for pure thought, written with specific symbols and modeled upon that of arithmetic (i.e., it develops according to definite rules). This is an essential difference between Frege’s calculus and, for example, Boole’s or Peano’s, which do not formalize mathematical proofs but are more flexible in expressing the logical structure of concepts.
One of Frege’s special symbols is the assertion sign (properly only the vertical stroke), which is in terpreted if followed by a symbol with judgeable content. The interpretation of A is “A is a fact.” Another symbol is the conditional , and is to be read as “B implies A.” The assertion is justified in the following cases: (1) A and B are true; (2) A is true and B is false; (3) A and B are false.
Frege uses only one deduction rule, which consists in passing from and to . The assertion that A is not a fact is expressed by i.e., the small vertical stroke is used for negation. Frege showed that the other propositional connectives, “and” and “or,” are expressible by means of negation and implication, and in fact developed propositional logic on the basis of a few axioms, some of which have been preserved in modern presentations of logic. Yet he did not stop at propositional logic but also developed quantification theory, which was possible because of his general notion of function. If in an expression a symbol was considered to be replaceable, in all or in some of its occurrences, then Frege calls the invariant part of the expression a function and the replaceable part its argument. He chose the expression Φ(A) for a function and, for functions of more than one argument, Ψ(A,B). Since the φ in φ(A) also may be considered to be the replaceable part, φ(A) may be viewed as a function of the argument φ. This stipulation proved to be the weak point in Frege’s system, as Russell showed in 1902.
Generality was expressed by
which means that φ(a) is a fact, whatever may be chosen for the argument. Frege explains the notion of the scope of a quantifier and notes the allowable transition from to , where a occurs only as argument of X(a), and from to , where a does not occur in A and in φ (a) occurs only in the argument places.
Existence was expressed by (a). There was no explicitly stated rule of substitution.
It should be observed that Frege did not construct his system for expressing pure thought as a formal system and therefore did not raise questions of completeness or consistency. Frege applied his Begriffsschrift to a general theory of sequences, and in part III he defines the ancestral relation on which he founded mathematical induction. This relation was afterward introduced informally by Dedekind and formally by Whitehead and Russell in Pricipia mathematica.
The Begriffsschrift essentially underlies Frege’s definition of number in Grundlagen der Arithmetik (1884), although it was not used explicitly. The greater part of this work is devoted to a severe and effective criticism of existing theories of number. Frege argues that number is something connected with an assertion concerning a concept; and essential for the notion of number is that of equality of number (i.e., he has to explain the sentence “The number which belongs to the concept F is the same as that which belongs to G.”). He settled on the definition “The number which belongs to the concept F is the extence of the concepts of beaing eqal to the concept F” where eqality of concepts is understood as the extension of a onetoone correspondence between their extensions. The number zero is that belonging to a concept with void extension, and the number one is that which belongs to the concept equal to zero. Using the notion of f sequence, natural numbers are defined, with ∞ the number belonging to the notion of being a natural number.^{1}
Frege’s theories, as well as his criticisms in the Begriffsschrift and the Grundlagen, were extended and refined in his Grundgesetze, in which he incorporated the essential improvements on his Begriffsschrift that had been expounded in the three important papers “Funktion und Begriff” (1891), “Über Sinn und Bedeutung” (1892), and “Über Begriff und Gegensstand” (1892). In particular, “Über Sinn und Bedeutung” is an essential complement to his Begriffsschrift. In addition, it has had a great influence on philosophical discussion, specifically on the development of Wittgenstein’s philosophy. Nevertheless, the philosophical implications of the acceptance of Frege’s doctrine have proved troublesome.
An analysis of the identity relation led Frege to the distinction between the sense of an expression and its denotation. If a and b are different names of the same object (refer to or denote the same object), we can legitimately express this by a = b, but = cannot be considered to be a relation between the objects themselves.
Frege therefore distinguishes two aspects of an expression: its denotation, which is the object to which it refers, and its sense, which is roughly the thought expressed by it. Every expression expresses its sense. An unsaturated expression (a function) has no denotation.
These considerations led Frege to the conviction that a sentence denotes its truthvalue; all true sentences denote the True and all false sentences denote the False—in other words, are names of the True and the False, respectively. The True and the False are to be treated as objects. The consequences of this distinction are further investigated in “Über Begriff und Gegenstand.” There Frege admits that he has not given a definition of concept and doubts whether this can be done, but he emphasizes that concept has to be kept carefully apart from object. More interesting developments are contained in his “Funktion und Begriff.” First, there is the general notion of fsequence already briefly mentioned in the Grundlagen, and second, with every function there is associated an object, the socalled Wertverlauf, which he used essentially in his Grundgesetze der Arithmetik.
Since a function is expressed by an unsaturated expression f(x), which denotes an object if x in it is replaced by an object, there arises the possibility of extending the notion of function because sentences denote objects (the True [T] and the False [F]), and one arrives at the conclusion that, e.g., (x^{2} = 4) = (x >1) is a function. If one replaces x by 1, then, because 1^{2} = 4 denotes F, as does 1 > 1, it follows that (1^{2} = 4) = (1 > 1) denotes T.
Frege distinguishes between firstlevel functions, with objects as argument, and secondlevel functions, with firstlevel functions as arguments, and notes that there are more possibilities. For Frege an object is anything which is not a function, but he admits that the notion of object cannot be logically defined. It is characteristic of Frege that he could not take the step of simply postulating a class of objects without entering into the question of their nature. This would have taken him in the direction of a formalistic attitude, to which he was fiercely opposed. In fact, at that time formalism was in a bad state and rather incoherently maintained. Besides, Frege was not creating objects but was concerned mainly with logical characterizations. This in a certain sense also holds true for Frege’s introduction of the Wertverlauf, which he believed to be something already there and which had to be characterized logically.
In considering two functions, e.g., x^{2} –4x and x(x–4), one may observe that they have the same value for the same argument. Therefore their graphs are the same. This situation is expressed by Frege true for Frege’s introduction of the Wertverlauf, as x^{2}–4x”. Without any further ado he goes on to speak of the Wertverlauf of a function as being something already there, and introduced a name for it. The Wertverläufe of the above mentioned functions x(x–4) and X^{2}4x are denoted by ὰ(α–4) and ὲ(ε^{2} — 4ε) respectively, and in general ὲf(ε) is used to denote the Wertverlauf of function f (ξ). This wertuerlauf is taken to be an object, and Frege assumes the basic logical law characterizing equality of Wertverläufe:
Frege extends this to logical functions (i.e., concepts), which are conceived of as functions whose values are truthvalues, and thus extension of a concept may be identified with the Wertverlauf of a function assuming only truthvalues. Therefore, e.g.,
In the appendix to volume II of his Grundgesetze, Frege derives Russell’s paradox in his system with the help of the above basic logical law. Russell later succeeded in eliminating his paradox by assuming the theory of types.
It is curious that the man who laid the most suitable foundation for formal logic was so strongly opposed to formalism. In volume II of the Grundgesetze, where he discusses formal arithmetic at length, Frege proves to have a far better insight than its exponents and justly emphasizes the necessity of a consistency proof to justify creative definitions. He is aware that because of the introduction of the Wertverläufe he may be accused of doing what he is criticizing. Nevertheless, he argues that he is not, because of his logical law concerning Wertverläufe (which proved untenable).
When Hilbert took the axiomatic method a decisive step further, Frege failed to grasp his point and attacked him for his imprecise terminology. Frege insisted on definitions in the classic sense and rejected Hilbert’s “definition” of a betweenness relation and his use of the term “point.” For Frege geometry was still the theory of space. But even before 1814 Bolzano had already reached the conclusion that for an abstract theory of space, one may be obliged to assume the term point as a primitive notion capable of various interpretations. Hilbert’s answer to Frege’s objections was quite satisfactory, although it did not convince Frege.
BIBLIOGRAPHY
I. Original Works. Frege’s writing includes Ueber eine geometrische Darstellung der imaginären Gebilde in der Ebene, his inaugural diss. to the Faculty of Philosophy at Göttingen (Jena, 1873); Begriffsschrift, eine der arithme tischen nachgebildete Formelsprache des reinen Denkens (Halle, 1879), 2nd ed., I. Angelelli, ed. (Hildesheim, 1964), English trans, in J. van Heijenoort, From Ferge to Godel (Cambridge, 1967), pp.1–82; Die Grundlagen der Arithmetik (Breslau, 1884), trans. with German text by J. L. Austin (Oxford, 1950; 2nd rev. ed. 1953), repr. as The Foundations of Arithmetic (Oxford, 1959); Function und Begriff (Jena, 1891), English trans. in P. Geach and M. Black, pp. 21–41 (see below); “Uber Sinn und Bedeutung,” in Zeitschrift für Philosophie und philosophische Kritik, n. s. 100 (1892) 25–50, English trans, in P. Geach and M. Black, pp. 56–78 (see below); “Über Begriff und Geogenstand” in Viertel jahrschrift für wissenschaftliche philosophie, 16 (1892) 192–205, English trans, in P. Geach and M. Black, pp. 42–55 (see below): Grundgesetze der Arithmetik, 2 vols. (Jena, 1893–1903), repr. in 1 vol. (Hildesheim, 1962); and “Über die Grundlagen der Geometrie in Jaheresbericht der Dutschen Mathematikervereinigung12 (1903) 319–324, 368–375; 15 (1906) 293–309, 377–403, 423–430
II. Secondary Literatrure. On Frege and his work, see I. Angelelli, Studies on Gottlob Frege and Traditional Philosophy (Dordrecht, 1967); P. Geach and M. Black, Translation of the Philosophical Writings of Gottlob Frege, 2nd ed. (oxford, 1960); H. Hermes, et al., Gottlob frege, Nachgelassene Schriften (Hamburg,1969); J. van Heijenfoort, From Frege to Godel (Cambridge, 1967): P. E. B. Jourdain, “The Development of the Theories of Mathematical Logic and the Principles of Mathematics. Gottlob Frege,” In Quarterly Journal of Pure and Applied Mathematics, 43 (1912), 237–269; W. Kneale and Martha Kneale, The Development of Logic (Oxford, 1962) pp. 435–512; J. Largeault, Logique et philosophie chez Frege (Paris–Louvain, 1970); C. Parsons, “Frege’s Theory of Number,” in M. Black, ed., Philosophy in America (London, 1965), pp. 180203; G. Patzig, Gottlob Frege, Funktion, Begriff, Bedeutung (Göttingem, 1966); and Gottlob Frege, Logische Untersuchungen (Göttingen, 1966); B. Russell, The Principles of Mathematics (Cambridge, 1903), Appendix A, “The Logical and Arithmetical Doctrines of Frege” M. Steck “Ein unbeakannter Brief von Gottlob Frege über Hilberts erste Vorlesung über die Grundlagen der Geometrie, in Sitzungsberichte der Heidelberger Akademie der Wissenschaften, Abhandlung 6 (1940); and “Unbekannte Briefe Frege’s über die Grundlagen der Geometrie und Antwort brief Hilbert’s and Frege ibid Abhandlung 2 (1941); H. G. Steiner, “Frege und die Grundlagen der Geometric I. II’ in Mathematischephysikalishce Semesterberichte, n. s. 10 (1963), 175–186 and 11 (1964), 35–47; and J. D. B. Walker, A Study of Frege (Oxford, 1965).
B. Van Rootselaar
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Gottlob Frege
Gottlob Frege
The German mathematician and philosopher Gottlob Frege (18481925) is considered the founder of modern mathematical logic. His work was almost wholly ignored during his lifetime but now exerts a great influence on the philosophy of logic and language.
Gottlob Frege was born on Nov. 8, 1848, at Wismar. He began his university studies at Jena in 1869 but after 2 years moved to Göttingen. He studied mathematics, the natural sciences, and philosophy and took his degree in 1873. Thereafter he taught at Jena in the department of mathematics. He was made a professor in 1896 and retired in 1918. Frege was married to Margarete Lieseberg, and the couple had one adopted son. Frege died on July 26, 1925, in Bad Kleinen.
Frege invented the concept of a formal system of mathematical logic, and in his first major work, Begriffsschrift (1879), he presented the first example of such a system in his formulation of a propositional and predicate calculus. He introduced the mathematical notion of function and variable into logic and invented the idea of quantifiers. He was also the first writer on axiomatic theory to make clear the distinction between an axiom and a rule of inference.
Further progress in this work convinced Frege that the basic ideas of arithmetic (but not of geometry) could be articulated solely in logical expressions. He expressed his new program first in a nonsymbolic work, The Foundations of Arithmetic (1884), which also featured a brilliant and devastating polemic against all previous attempts at the subject. The crown of his work was to be his Basic Laws of Arithmetic. The first volume of this work appeared in 1893; but in 1903, as Frege was about to issue the second volume, Bertrand Russell pointed out a contradiction in Frege's use of the concept of a "class," which undermined the proofs in the work. Frege hastily added an appendix that sought to remedy the defect (this effort was later proved defective), but thereafter he seemed to lose interest in the great project. Two decades later he regarded the whole enterprise as an error and fell back upon the Kantian interpretation of mathematical judgments as synthetic a priori.
Frege also made important contributions to the philosophy of logic. Concerning the old question: what is it for a proposition to have meaning?—he introduced a variety of distinctions that are being exploited by contemporary philosophers. Frege rejected epistemology as the starting point of philosophy and revived the classical view, dominant before René Descartes, that philosophical logic holds this place.
Further Reading
There are no biographies of Frege. His work, however, has been extensively studied, especially since translations of it have become available, beginning in the 1950s. A convenient collection of most of the important critical essays is in E. D. Klemke, ed., Essays on Frege (1968), which also has a complete bibliography. Two difficult but rewarding fulllength studies are Jeremy D. B. Walker, A Study of Frege (1965), and Robert Sternfeld, Frege's Logical Theory (1966). □
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Frege, Gottlob
Gottlob Frege (gôt´lōp frā´gə), 1848–1925, German philosopher and mathematician. He was professor of mathematics (1879–1918) at the Univ. of Jena. Frege was one of the founders of modern symbolic logic, and his work profoundly influenced Bertrand Russell. He claimed that all mathematics could be derived from purely logical principles and definitions. He considered verbal concepts to be expressible as symbolic functions with one or more variables. His books include Begriffsschrift (1879); Die Grundlagen der Arithmetik (1884; tr. The Foundations of Arithmetic, 1950); Grundgesetze der Arithmetik (2 vol., 1893–1903).
See P. T. Geach and M. Black, ed., Philosophical Writings of Gottlob Frege (1952); M. Resnik, Frege and the Philosophy of Mathematics (1980); M. Dummett, The Interpretation of Frege's Philosophy (repr. 1981).
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Frege, Gottlob
Frege, Gottlob (1848–1925) German philosopher, professor of mathematics at the University of Jena (1879–1918). With George Boole, Frege was one of the founders of modern symbolic logic. In his Foundations of Arithmetic (1884), Frege attempted to derive all mathematics from logical axioms.
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