Mathematicians often speak of conjectures, yet unproved, as probable or well-confirmed by evidence. The Riemann Hypothesis, for example, is widely believed to be almost certainly true. There seems no initial reason to distinguish such probability from the same notion in empirical science. Yet it is hard to see how there could be probabilistic relations between the necessary truths of pure mathematics. The existence of such logical relations, short of certainty, is defended using the theory of logical probability (or objective Bayesianism (...) or non-deductive logic), and some detailed examples of its use in mathematics surveyed. Examples of inductive reasoning in experimental mathematics are given and it is argued that the problem of induction is best appreciated in the mathematical case. (shrink)

ArgumentThe Fourth Postulate of Euclid’s Elements states that all right angles are equal. This principle has always been considered problematic in the deductive economy of the treatise, and even the ancient interpreters were confused about its mathematical role and its epistemological status. The present essay reconsiders the ancient testimonies on the Fourth Postulate, showing that there is no certain evidence for its authenticity, nor for its spuriousness. The paper also considers modern mathematical interpretations of this postulate, pointing out various anachronisms. (...) It further discusses the validity of the ancient proof by superposition of the Fourth Postulate. Finally, the article proposes an interpretation of the history of the concept of angle in Greek geometry between Euclid and Apollonius, and puts forward a conjecture on the interpolation of the Fourth Postulate in the Hellenistic age. The essay contributes to a general reassessment of the axiomatic foundations of ancient mathematics. (shrink)

Pour rendre compte de la première démonstration d’existence d’une grandeur irrationnelle, les historiens des sciences et les commentateurs d’Aristote se réfèrent aux textes sur l’incommensurabilité de la diagonale qui se trouvent dans les Premiers Analytiques, les plus anciens sur la question. Les preuves usuelles proposées dérivent d’un même modèle qui se trouve à la fin du livre X des Éléments d’Euclide. Le problème est que ses conclusions, passant par la représentation des fractions comme rapport de deux entiers premiers entre eux, (...) i.e. la proposition VII.22 des Éléments, ne correspondent pas aux écrits aristotéli­ciens. Dans cet article, nous proposons une nouvelle démonstration, conforme aux textes des Analytiques, fondés sur des résultats très anciens de la théorie du pair et de l’impair. Ne passant pas par la proposition VII.22, ni par aucune autre propriété établie par l’absurde, cette irrationalité apparaît comme le premier résultat que l’on ne pouvait établir par une autre méthode. L’importance de ce résultat, révélant un nouveau domaine mathématique, celui des grandeurs irrationnelles, rend compte de la centralité que cette forme de raisonnement acquiert alors, d’abord en mathématique, puis dans tout type de discours rationnel. À partir des conséquences qui suivent de cette nouvelle démonstration, on peut interpréter très simplement la leçon sur les irrationnels du passage mathématique figurant dans le Théétète de Platon (147d-148b), ce que nous ferons dans un article à paraître dans un prochain numéro. (shrink)

We provide a new interpretation of Zeno’s Paradox of Measure that begins by giving a substantive account, drawn from Aristotle’s text, of the fact that points lack magnitude. The main elements of this account are (1) the Axiom of Archimedes which states that there are no infinitesimal magnitudes, and (2) the principle that all assignments of magnitude, or lack thereof, must be grounded in the magnitude of line segments, the primary objects to which the notion of linear magnitude applies. Armed (...) with this account, we are ineluctably driven to introduce a highly constructive notion of (outer) measure based exclusively on the total magnitude of potentially infinite collections of line segments. The Paradox of Measure then consists in the proof that every finite or potentially infinite collection of points lacks magnitude with respect to this notion of measure. We observe that the Paradox of Measure, thus understood, troubled analysts into the 1880’s, despite their knowledge that the linear continuum is uncountable. The Paradox was ultimately resolved by Borel in his thesis of 1893, as a corollary to his celebrated result that every countable open cover of a closed line segment has a finite sub-cover, a result he later called the “First Fundamental Theorem of Measure Theory.” This achievement of Borel has not been sufficiently appreciated. We conclude with a metamathematical analysis of the resolution of the paradox made possible by recent results in reverse mathematics. (shrink)

In the eighth chapter of De Sophisticis Elenchis, Aristotle introduces a mode of sophistical refutation that constitutes an addition to the taxonomy of the earlier chapters of the treatise. The new mode is pseudo-scientific refutation, or “the [syllogism or refutation] which though real, [merely] appears appropriate to the subject matter”. Against the grain of its most commonly accepted reading, I argue that Aristotle is not concerned in SE 8 to establish that both the apparent refutations of SE 4–7 and pseudo-scientific (...) refutations issue in false conclusions. His concern rather is to provide a causal analysis of both classes of apparent refutation alike which will explain why both kinds of apparent refutation are sophistical – and whose solutions are therefore the task of no special science but of a dialectical σλλογιστιϰή τέχνη. I conclude my analysis with the observation that Aristotle exploits the results of SE 8 to fend off inSE 9, 10, and 11 respectively a triad of threats to the very existence of a τέχνη of the resolution of sophistical refutation. The three threats are: the impossibility of omniscience; the relativity of semantic beliefs; and the incapacity of a questioner ignorant of a science to expose the ignorance of a pretender to scientific expertise. (shrink)

This article focusses on the generality of the entities involved in a geometric proof of the kind found in ancient Greek treatises: it shows that the standard modern translation of Greek mathematical propositions falsifies crucial syntactical elements, and employs an incorrect conception of the denotative letters in a Greek geometric proof; epigraphic evidence is adduced to show that these denotative letters are ‘letter-labels’. On this basis, the article explores the consequences of seeing that a Greek mathematical proposition is fully general, (...) and the ontological commitments underlying the stylistic practice. (shrink)

The purpose of this work is to address the relation existing between ancient Greek practical geometry and ancient Greek pure geometry. In the first part of the work, we will consider practical and pure geometry and how pure geometry can be seen, in some respects, as arising from an idealization of practical geometry. From an analysis of relevant extant texts, we will make explicit the idealizations at play in pure geometry in relation to practical geometry, some of which are basically (...) explicit in definitions, like that of segments in Euclid’s Elements. Then, we will address how in pure geometry we, so to speak, “refer back” to practical geometry. This occurs in two ways. One, in the propositions of pure geometry. The other, when applying pure geometry. In this case, geometrical objects can represent practical figures like, e.g., a practical segment. (shrink)

A form of quantification logic referred to by the author in earlier papers as being 'ontologically neutral' still made use of the actual infinite in its semantics. Here it is shown that one can have, if one desires, a formal logic that refers in its semantics only to the potential infinite. Included are two new quantifiers generalizing the sentential connectives, equivalence and non-equivalence. There are thus new avenues opening up for exploration in both quantification logic and semantics of the infinite.

At Aristotle,MetaphysicsE.1, 1026a14, Schwegler’s conjectural emendation of the manuscript reading ἀχώριστα to χωριστά has been widely adopted. The objects of physical science are therefore here ‘separate’, or ‘independently existent’. By contrast, the manuscripts make them ‘not separate’, construed by earlier commentators as dependent on matter. In this paper, I offer a new defense of the manuscript reading. I review past defenses based on the internal consistency of the chapter, explore where they have left supporters of the emendation unpersuaded, and attempt (...) to strengthen their appeal. I challenge Schwegler’s central case, developed by Ross and others, that the construction μὲν ἀλλ’ οὐκ demands an implausible ‘logical antithesis’ between inseparability and mobility. This is arguably the fundamental obstacle to the manuscript reading, and counterexamples have not to date convinced emenders. I offer a new, systematic review of Aristotle’s use of the phrase, including relevant cases from theRhetoric, to show how its usual meaning in Aristotle supports the transmitted text; I also reply to possible objections. Finally, I explore the implications of this defense for the classification of the sciences in E.1. (shrink)

This paper aims to show that an examination of some passages in Aristotle’s work can contribute to the resolution of crucial problems related to the interpretation of ancient geometrical analysis. In this context, we will focus in particular on the famous passage of the Posterior Analytics in which Aristotle cryptically refers to the analysis practised by the geometers and we will show the fundamental importance of this passage for a correct understanding of ancient geometrical analysis.

I present a systematic interpretation of the foundational purpose of constructions in ancient Greek geometry. I argue that Greek geometers were committed to an operationalist foundational program, according to which all of mathematics—including its entire ontology and epistemology—is based entirely on concrete physical constructions. On this reading, key foundational aspects of Greek geometry are analogous to core tenets of 20th-century operationalist/positivist/constructivist/intuitionist philosophy of science and mathematics. Operationalism provides coherent answers to a range of traditional philosophical problems regarding classical mathematics, such (...) as the epistemic warrant and generality of diagrammatic reasoning, superposition, and the relation between constructivism and proof by contradiction. Alleged logical flaws in Euclid can be interpreted as sound operationalist reasoning. Operationalism also provides a compelling philosophical motivation for the otherwise inexplicable Greek obsession with cube duplication, angle trisection, and circle quadrature. Operationalism makes coherent sense of numerous specific choices made in this tradition, and suggests new interpretations of several solutions to these problems. In particular, I argue that: Archytas’s cube duplication was originally a single-motion machine; Diocles’s cissoid was originally traced by a linkage device; Greek conic section theory was thoroughly constructive, based on the conic compass; in a few cases, string-based constructions of conic sections were used instead; pointwise constructions of curves were rejected in foundational contexts by Greek mathematicians, with good reason. Operationalism enables us to view the classical geometrical tradition as a more unified and philosophically aware enterprise than has hitherto been recognised. (shrink)

With the systematic aim of clarifying the phenomenon sometimes described as “the intellectual apprehension of first principles,” Descartes’ first principle par excellence is interpreted before the historical backcloth of Aristotle’s Posterior Analytics. To begin with, three “faces” of the cogito are distinguished: (1) the proto-cogito (“I think”), (2) the cogito proper (“I think, therefore I am”), and (3) the cogito principle (“Whatever thinks, is”). There follows a detailed (though inevitably somewhat conjectural) reconstruction of the transition of the mind from (1) (...) via (3) to (2) and back again to (3). What emerges is, surprisingly, a non-circular, non-logical, and ultimately non-mysterious process by which first principles implicitly contained in a complex intuition are gradually rendered explicit (and, if abstract, grasped in their abstract universality). This process bears a striking family resemblance to that intuitive induction (“grasping the universal in the particular”) which Aristotle scholars have distinguished from empirical forms of induction. (shrink)

In a recent paper Johan van Benthem reviews earlier work done by himself and colleagues on ‘natural logic’. His paper makes a number of challenging comments on the relationships between traditional logic, modern logic and natural logic. I respond to his challenge, by drawing what I think are the most significant lines dividing traditional logic from modern. The leading difference is in the way logic is expected to be used for checking arguments. For traditionals the checking is local, i.e. separately (...) for each inference step. Between inference steps, several kinds of paraphrasing are allowed. Today we formalise globally: we choose a symbolisation that works for the entire argument, and thus we eliminate intuitive steps and changes of viewpoint during the argument. Frege and Peano recast the logical rules so as to make this possible. I comment also on the traditional assumption that logical processing takes place at the top syntactic level, and I question Johan’s view that natural logic is ‘natural’. (shrink)

Reagere, reactio does not belong to classical Latin. Reagere appears, as late as the fourth century A.D., in Avienus, but not reactio. Nonetheless, antiquity was not unaware of the concept of reciprocal action, where the “patient” reacts in return on the agent. The Aristotelian doctrine of antiperistasis occupied physicists up until the time of Galileo: “All movers, as long as they move, are at the same time moved.” The Latin authors dispense with reagere and reactio. It is the verb pati, (...) designating the passive state to which the prefix re is added in the aphorism attributed to the Scholastics in the 18th century dictionaries: omnis agens agendo repatitur. (shrink)

We discuss the concept of a cardinal number and its history, focussing on Cantor's work and its reception. J'ay fait icy peu pres comme Euclide, qui ne pouvant pas bien >faire< entendre absolument ce que c'est que raison prise dans le sens des Geometres, definit bien ce que c'est que memes raisons. (Leibniz) 1.

To justify certain steps of the computation developed in his Sand-Reckoner, Archimedes cites the following inequalities relative to the sides of right triangles: if of two right-angled triangles, the sides about the right angle are equal , while the other sides are unequal, the greater angle of those toward [sc. next to] the unequal sides has to the lesser a greater ratio than the greater line of those subtending the right angle to the lesser, but a lesser than the greater (...) line of those about the right angle to the lesser. That is, with reference to the two right triangles ABG, DEZ , where AG equals DZ and the angle at B is greater than that at E, ZE:GB < angle B:angle E < DE:AB. (shrink)

This article proposes an interpretation of the chapters of theNicomachean Ethicsconcerning exchange and friendship. Rejecting approaches where Aristotle anticipates modern labour or need-based theories of value, the article claims that those notions of labour and need are required for a satisfactory interpretation of the most obscure passages of Book V. Finally, Aristotle's texts on exchange and friendship are related in such a way that the latter, since it is free from any political considerations, allows us to better understand the philosopher's (...) view on exchange. (shrink)

Through a detailed analysis of the various modes of argumentation employed by Aristotle throughout his natural scientific works, I aim to contribute to the growing scholarship on the relation between Aristotle’s theory of science and his actual scientific practice. I challenge the standard reading of Aristotle as a methodological empiricist and show that he permits a variety of non-empirical arguments to support controversial theses in properly scientific contexts. Specifically, I examine his use of logical (logikôs) argumentation in the discussion of (...) mule sterility in Generation of Animals II 8, rational (kata ton logon) argumentation in his discussion of cardiocentrism throughout the biological works, and the method of division in Posterior Analytics II 13. (shrink)