This entry introduces the reader to the main ideas in Frege's philosophy of logic, mathematics, and language.

This open access book is a superb collection of some fifteen chapters inspired by Schroeder-Heister's groundbreaking work, written by leading experts in the field, plus an extensive autobiography and comments on the various contributions by Schroeder-Heister himself. For several decades, Peter Schroeder-Heister has been a central figure in proof-theoretic semantics, a field of study situated at the interface of logic, theoretical computer science, natural-language semantics, and the philosophy of language. -/- The chapters of which this book is composed discuss the (...) subject from a rich variety of angles, including the history of logic, the proper interpretation of logical validity, natural deduction rules, the notions of harmony and of synonymy, the structure of proofs, the logical status of equality, intentional phenomena, and the proof theory of second-order arithmetic. All chapters relate directly to questions that have driven Schroeder-Heister's own research agenda and to which he has made seminal contributions. The extensive autobiographical chapter not only provides a fascinating overview of Schroeder-Heister's career and the evolution of his academic interests but also constitutes a contribution to the recent history of logic in its own right, painting an intriguing picture of the philosophical, logical, and mathematical institutional landscape in Germany and elsewhere since the early 1970s. The papers collected in this book are illuminatingly put into a unified perspective by Schroeder-Heister's comments at the end of the book. Both graduate students and established researchers in the field will find this book an excellent resource for future work in proof-theoretic semantics and related areas. (shrink)

What is the relationship between the world and logic, between intuition and language, between objects and their quantitative determinations? Rationalists, on the one hand, hold that the world is structured in a rational way. Representationalists, on the other hand, assume that language, logic, and mathematics are only the means to order and describe the intuitively given world. In World and Logic, Jens Lemanski takes up three surprising arguments from Arthur Schopenhauer’s hitherto undiscovered Berlin Lectures, which concern the philosophy of language, (...) logic, and mathematics. Based on these arguments, Lemanski develops a new position entitled ‘rational representationalism’: the world is always structured by human beings according to linguistic, logical, and mathematical principles, but the basic vocabulary of these structural descriptions already contains metaphors taken from the world around us. (shrink)

In this extended essay, I argue that Frege plagiarized the Stoics --and I mean exactly that-- on a large scale in his work on the philosophy of logic and language as written mainly between 1890 and his death in 1925 (much of which published posthumously) and possibly earlier. I use ‘plagiarize' (or 'plagiarise’) merely as a descriptive term. The essay is not concerned with finger pointing or casting moral judgement. The point is rather to demonstrate carefully by means of detailed (...) evidence that there are numerous (over a hundred) and extensive parallels both in formulation and --more importantly-- in content between the Stoics and Frege, parallels so plentiful that one would be hard pressed to brush them off as coincidence. These parallels include several that appear to occur in no other modern works that were published before Frege’s own and were accessible to him. Additionally, a cluster of corroborating historical data is adduced to support the suggestion, showing how easy it would have to been for Frege to plagiarize the Stoics. This (first) part of the essay is easy to read and vaguely entertaining, or so I hope. -/- (Corrigendum: At school, Frege likely had seven, not ten, years of intensive Latin and four years of intensive ancient Greek courses.). (shrink)

I critically discuss Dale Jacquette’s Frege: A Philosophical Biography. First, I provide a short overview of Jacquette’s book. Second, I evaluate Jacquette’s interpretation of Frege’s three major works, Begriffsschrift, Grundlagen der Arithmetik and Grundgesetze der Arithmetik; and conclude that the author does not faithfully represent their content. Finally, I offer some technical and general remarks.

The purpose of this study is to assess Husserl’s debt to Lotze’s philosophy during the Halle period (1886-1901). I shall first track the sources of Husserl’s knowledge of Lotze’s philosophy during his studies with Brentano in Vienna and then with Stumpf in Halle. I shall then briefly comment on Husserl’s references to Lotze in his early work and research manuscripts for the second volume of his Philosophy of Arithmetic. In the third section, I examine Lotze’s influence on Husserl’s antipsychologistic turn (...) in the mid-1890s. The fourth section is a commentary on Husserl’s manuscript entitled “Microcosmus,” to which he explicitly refers in his Prolegomena, and which he planned to publish as an annex of his Logical Investigations. This work contains a detailed analysis of the third book of Lotze’s 1874 Logic. The last section examines Husserl’s arguments against logical psychologism in his Prolegomena, which I discuss through the lens of Stumpf’s critique of psychologism in his paper “Psychology and theory of knowledge”. I argue that Stumpf’s early works on this topic make it possible to establish a connection between Lotze’s interpretation of Plato’s theory of Ideas and Husserl’s antipsychologism. My hypothesis is that Stumpf’s analyses represent the background of Husserl's critique of logical psychologism in his Logical Investigations. I shall conclude this study by showing that Husserl’s position with respect to Lotze’s philosophy remains basically unchanged after the publication of his Logical Investigations, and that Husserl’s main criticism of Lotze pertains, in the final analysis, to the absence of a theory of intentionality in Lotze’s philosophy. (shrink)

El propósito del presente estudio es afirmar la deuda de Husserl con la filosofía de Lotze durante el período de Halle. Mi interés se centra especialmente en el pensamiento del joven Husserl desde su llegada a Halle en 1886 hasta la publicación de su Hauptwerk en 1900-1901. Primero me remontaré a las fuentes del conocimiento de la filosofía de Lotze por parte de Husserl durante sus estudios con Brentano en Viena y después con Stumpf en Halle. Luego comentaré brevemente las (...) referencias de Husserl a Lotze en sus primeros trabajos y en sus manuscritos de investigación para el segundo volumen de su Filosofía de la aritmética. En la tercera sección, examino la influencia de Lotze en el giro antipsicologista de Husserl a mediados de la década de 1890. La cuarta sección es un comentario al manuscrito de Husserl titulado "Microcosmos", al cual se refiere explícitamente en sus Prolegómenos, y que planeaba publicar como anexo a sus Investigaciones lógicas. Esta obra contiene un análisis detallado del tercer volumen de la Lógica de Lotze de 1874. La última sección examina los argumentos de Husserl contra el psicologismo lógico en sus Prolegómenos, que yo expongo a través del prisma de la crítica de Stumpf al psicologismo en su artículo "Psicología y teoría del conocimiento". Sostengo que las primeras obras de Stumpf sobre este asunto hacen posible establecer una conexión entre la interpretación de Lotze de la teoría de las Ideas de Platón y el antipsicologismo de Husserl. Mi hipótesis es que los análisis de Stumpf representan el fondo de la crítica de Husserl al psicologismo lógico en sus Investigaciones lógicas. Concluiré este estudio mostrando que la posición de Husserl respecto de la filosofía de Lotze permanece básicamente la misma después de la publicación de sus Investigaciones lógicas, y que la principal crítica de Husserl a Lotze se refiere, en un último análisis, a la ausencia de una teoría de la intencionalidad en la filosofía de Lotze. (shrink)

Well over a century after its introduction, Frege's two-dimensional Begriffsschrift notation is still considered mainly a curiosity that stands out more for its clumsiness than anything else. This paper focuses mainly on the propositional fragment of the Begriffsschrift, because it embodies the characteristic features that distinguish it from other expressively equivalent notations. In the first part, I argue for the perspicuity and readability of the Begriffsschrift by discussing several idiosyncrasies of the notation, which allow an easy conversion of logically equivalent (...) formulas, and presenting the notation's close connection to syntax trees. In the second part, Frege's considerations regarding the design principles underlying the Begriffsschrift are presented. Frege was quite explicit about these in his replies to early criticisms and unfavorable comparisons with Boole's notation for propositional logic. This discussion reveals that the Begriffsschrift is in fact a well thought-out and carefully crafted notation that intentionally exploits the possibilities afforded by the two-dimensional medium of writing like none other. (shrink)

The impartial reader notices that Frege, in Die Verneinung, treats an opposing conception of negation, but without specifically naming its proponent. In this paper, it is proven for the first time that the view in question is that of his colleague in Jena, Bruno Bauch. Besides their different views, concerning above all the status of false thoughts, there are nonetheless broader points of agreement between the ideas of Bauch and Frege. These points of agreement cast light on both thinkers as (...) representatives of a current of Neo-Kantianism, having its source in Lotze, in which Kantian and Platonic elements are fused to form a ?transcendental Platonism? (shrink)

In recent years, several scholars have been investigating Frege’s mathematical background, especially in geometry, in order to put his general views on mathematics and logic into proper perspective. In this article I want to continue this line of research and study Frege’s views on geometry in their own right by focussing on his views on a field which occupied center stage in nineteenth century geometry, namely, projective geometry.

The aim of this article is to contribute to a better understanding of Frege’s views on semantics and metatheory by looking at his take on several themes in nineteenth century geometry that were significant for the development of modern model-theoretic semantics. I will focus on three issues in which a central semantic idea, the idea of reinterpreting non-logical terms, gradually came to play a substantial role: the introduction of elements at infinity in projective geometry; the study of transfer principles, especially (...) the principle of duality; and the use of counterexamples in independence arguments. Based on a discussion of these issues and how nineteenth century geometers reflected about them, I will then look into Frege’s take on these matters. I conclude with a discussion of Frege’s views and what they entail for the debate about his stance towards semantics and metatheory more generally. (shrink)

I offer in this paper a contextual analysis of Frege's Grundlagen, section 64. It is surprising that with so much ink spilled on that section, the sources of Frege's discussion of definitions by abstraction have remained elusive. I hope to have filled this gap by providing textual evidence coming from, among other sources, Grassmann, Schlömilch, and the tradition of textbooks in geometry for secondary schools . In addition, I put Frege's considerations in the context of a widespread debate in Germany (...) on ‘directions’ as a central notion in the theory of parallels. (shrink)

It has been noted before in the history of logic that some of Frege's logical and semantic views were anticipated in Stoicism. In particular, there seems to be a parallel between Frege's Gedanke (thought) and Stoic lekton; and the distinction between complete and incomplete lekta has an equivalent in Frege's logic. However, nobody has so far claimed that Frege was actually influenced by Stoic logic; and there has until now been no indication of such a causal connection. In this essay, (...) we attempt, for the first time, to provide detailed evidence for the existence of this connection. In the course of our argumentation, further analogies between the positions of Frege and the Stoics will be revealed. The classical philologist Rudolf Hirzel will be brought into play as the one who links Frege with Stoicism. The renowned expert on Stoic philosophy was Frege's tenant and lived in the same house as the logician for many years. In der Geschichte der Logik ist häufig bemerkt worden, dass einige der logischen und semantischen Auffassungen Freges in der Stoa antizipiert worden sind. Genannt wurden insbesondere die Parallelen zwischen dem Fregeschen Gedanken und dem stoischen Lekton sowie die Unterscheidung zwischen vollständigen und unvollständigen Lekta, die bei Frege ihre Entsprechung hat. Ein Wirkungszusammenhang ist allerdings nicht behauptet worden. Dazu gab es bislang auch keinen Anlass. Der vorliegende Beitrag versucht erstmalig, einen detaillierten Indizienbeweis für das Bestehen eines solchen Zusammenhangs vorzulegen. Dabei werden weitere charakteristische Übereinstimmungen zwischen Frege und der Stoa aufgewiesen. Als Mittelsmann wird der Altphilologe Rudolf Hirzel vorgestellt. Er wohnte lange Jahre als Mieter zusammen mit Frege im selben Haus und war ein anerkannter Experte der stoischen Philosophie. (shrink)

A running commentary is offered on the first half of Frege’s Grundlagen der Arithmetik, §17, and suggests that Frege anticipated the method of demonstration used by Paul Bernays for the Deduction Theorem.

This paper has a two-fold objective: to provide a balanced, multi-faceted account of the origins of logicism; to rehabilitate Richard Dedekind as a main logicist. Logicism should be seen as more deeply rooted in the development of modern mathematics than typically assumed, and this becomes evident by reconsidering Dedekind's writings in relation to Frege's. Especially in its Dedekindian and Fregean versions, logicism constitutes the culmination of the rise of ?pure mathematics? in the nineteenth century; and this rise brought with it (...) an inter-weaving of methodological and epistemological considerations. The latter aspect illustrates how philosophical concerns can grow out of mathematical practice, as opposed to being imposed on it from outside. It also sheds new light on the legacy and the lasting significance of logicism today. (shrink)

Setting out to understand Frege, the scholar confronts a roadblock at the outset: We just have little to go on. Much of the unpublished work and correspondence is lost, probably forever. Even the most basic task of imagining Frege's intellectual life is a challenge. The people he studied with and those he spent daily time with are little known to historians of philosophy and logic. To be sure, this makes it hard to answer broad questions like: 'Who influenced Frege?' But (...) the information vacuum also creates local problems of textual interpretation. Say we encounter a sentence that may be read as alluding to a scientific dispute. Should it be read that way? To answer, we'd need to address prior questions. Is it .. (shrink)

Há muitos pontos de concordância entre Frege e os neokantianos. Isso vale especialmente para os representantes do neokantismo da teoria do valor ou do Sudoeste alemão na tradição de Hermann Lotze. Não discutiremos aqui todos os aspectos dessa proximidade; de acordo com o tema que propomos, ficaremos restritos à filosofia da matemática. A primeira parte do artigo tratará da relação entre aritmética e geometria, mostrando surpreendentes semelhanças entre Frege e o neokantiano Otto Liebmann. A segunda parte discutirá as diferentes recepções (...) do logicismo de Frege por Jonas Cohn, Paul Natorp, Heinrich Rickert, Ernst Cassirer e Bruno Bauch. (shrink)