Paola Cantù

The paper aims to establish if Grassmann’s notion of an extensive form involved an epistemological change in the understanding of geometry and of mathematical knowledge. Firstly, it will examine if an ontological shift in geometry is determined by the vectorial representation of extended magnitudes. Giving up homogeneity, and considering geometry as an application of extension theory, Grassmann developed a different notion of a geometrical object, based on abstract constraints concerning the construction of forms rather than on the homogeneity conditions required by the modern version of the theory of proportions. Secondly, Grassmann’s conception of mathematical knowledge will be investigated. Parting from the traditional definition of mathematics as a science of magnitudes, Grassmann considered mathematical forms as particulars rather than universals: the classification of the branches of mathematics was thus based on different operational rules, rather than on empirical criteria of abstraction or on the distinction of different species belonging to a common genus. It will be argued that a different notion of generalization is thus involved, and that the knowledge of mathematical forms relies on the understanding of the rules of generation of the forms themselves. Finally, the paper will analyse if Grassmann’s approach in the first edition of the Ausdehnungslehre should be explained in terms of the notion of purity of method, and if it clashes with Grassmann’s later conventionalism. Although in the second edition the features of the operations are chosen by convention, as it is the case for the anti-commutative property of the multiplication, the choice is oriented by our understanding of the resulting forms: a simplification in the algebraic calculus need not correspond to a simplification in the ‘dimensional’ interpretation of the result of the multiplicative operation.

L'article aborde la question suivante : est-ce que le bon ordre des concepts peut être considéré un élément essentiel de rigueur scientifique dans la logique et les mathématiques de xixe et xxe siècle, en particulier quand il s'agit d'auteurs qui ont été influencés profondément par le projet leibnizien de la caractéristique? L'article prend en considération trois exemples : Hermann Graßmann, Giuseppe Peano et Kurt Gödel. Selon notre thèse, le choix des concepts primitifs dans les théories hypothético-déductives n'était pas seule­ment une question d'opportunité, mais parfois aussi le résultat d'une investiga­tion philosophique sur les fondements des disciplines scientifiques. La question du « bon » ordre des concepts n'est plus considérée comme une tâche réalisable, maïs elle est devenue un idéal à suivre ; néanmoins elle reste une partie essen­tielle du travail axiomatique. L'article vise donc à critiquer l'opposition trop nette qu'on trouve dans la littérature entre l'investigation de l'âge classique sur le bon ordre des concepts et la création de l'axiomatique moderne. La rup­ture scientifique déterminée par la création des systèmes axiomatico-deductifs en mathématiques et logique doit donc être associée à certains éléments de continuité qui regardent l'idéal de la connaissance en tant que recherche d'une théorie générale des concepts à obtenir par composition de certains éléments fondamentaux.

At the beginning of the xxth century the high rate of analphabetism and the recent unification of the country, achieved only in 1870, had required a vast program of school and university reforms which were accompanied by a debate on two fundamental questions: whether the university should depend on public funds or become autonomous, and whether the curriculum should be specialized or remain general as in the modern era. The 1859 Casati reform had separated the faculty for literature and philosophy from the faculty for mathematical, physical and natural sciences, thus introducing for the first time specialized curricula.

The article evaluates the Domain Postulate of the Classical Model of Science and the related Aristotelian prohibition rule on kind-crossing as interpretative tools in the history of the development of mathematics into a general science of quantities. Special reference is made to Proclus’ commentary to Euclid’s first book of Elements, to the sixteenth century translations of Euclid’s work into Latin and to the works of Stevin, Wallis, Viète and Descartes. The prohibition rule on kind-crossing formulated by Aristotle in Posterior analytics is used to distinguish between conceptions that share the same name but are substantively different: for example the search for a broader genus including all mathematical objects; the search for a common character of different species of mathematical objects; and the effort to treat magnitudes as numbers.

The paper analyses the role played by the concept of ‘common ground’ in argumentation theories. If a common agreement on all the rules of a discursive exchange is required, either at the beginning or at the end of an argumentative practice, then no violation of the rules is possible. The paper suggests an alternative understanding of ‘common ground’ as something that can change during the development of the argumentative practice, and in particular something that can change without the practice being stopped, just as one sometimes violates the rule of a game without stopping playing. The analysis of some historical examples shows that the violation of rules sometimes leads to a consensual change of a set of beliefs and values. The argumentative rationality thus needs to be reconsidered in the light of the analysis of the conditions under which it would be legitimate to change the rules of an argumentative practice: ‘common ground’ and the right to disagreement, even radical or violent, could then be defended as essential components of argumentative rationality.

Argumentation theory underwent a significant development in the Fifties and Sixties: its revival is usually connected to Perelman's criticism of formal logic and the development of informal logic. Interestingly enough it was during this period that Artificial Intelligence was developed, which defended the following thesis (from now on referred to as the AI-thesis): human reasoning can be emulated by machines. The paper suggests a reconstruction of the opposition between formal and informal logic as a move against a premise of an argument for the AI-thesis, and suggests making a distinction between a broad and a narrow notion of algorithm that might be used to reformulate the question as a foundational problem for argumentation theory.