Mikko Yrjönsuuri

Could formal logic be a naturalist field of study? This paper analyses how medieval logicians committed to Aristotelian naturalism thought about the metaphysical grounding of logic. As they assumed, it is at least sometimes a fact that a conclusion follows from some premises; here it is questioned how they thought this fact, or logical validity, to be grounded. The early medieval Arabic tradition (e.g. Ibn Sinā) thought in a way comparable to Immanuel Kant’s position that logic is a formal study of intellectual structures, but given their metaphysical realism concerning universals, such intellectual structures may be taken to be natural parts of Aristotelian metaphysics. On the other hand, the early medieval Latin tradition (e.g. Abelard) thought in a way comparable to Bernard Bolzano that the subject matter logic studies is not the intellectual realm, but essentially linguistic facts, taking language to be a natural phenomenon. Robert Kilwardby endeavoured to combine these traditions, but turns out to have taken a stance much closer to Kant, and to have given little importance to linguistic facts in his account of how syllogistic validity and thereby validity in general is grounded. At the same time, Kilwardby’s work enhanced the conception of the formality of logic, although he thought that only the syllogistic form is a properly logical form. Analysis of John Buridan’s logic shows that he had a generalized conception of logical form that was tightly knit with linguistic form as it is found in mental language, which he took to be a metaphysically natural domain. Unlike Kant and Bolzano, both Kilwardby and Buridan can be viewed as naturalists as concerns the study of formal logic, inasmuch as they thought that logical validity is grounded in facts that their Aristotelian metaphysics would consider natural.

Could formal logic be a naturalist field of study? This paper analyses how medieval logicians committed to Aristotelian naturalism thought about the metaphysical grounding of logic. As they assumed, it is at least sometimes a fact that a conclusion follows from some premises; here it is questioned how they thought this fact, or logical validity, to be grounded. The early medieval Arabic tradition (e.g. Ibn Sinā) thought in a way comparable to Immanuel Kant’s position that logic is a formal study of intellectual structures, but given their metaphysical realism concerning universals, such intellectual structures may be taken to be natural parts of Aristotelian metaphysics. On the other hand, the early medieval Latin tradition (e.g. Abelard) thought in a way comparable to Bernard Bolzano that the subject matter logic studies is not the intellectual realm, but essentially linguistic facts, taking language to be a natural phenomenon. Robert Kilwardby endeavoured to combine these traditions, but turns out to have taken a stance much closer to Kant, and to have given little importance to linguistic facts in his account of how syllogistic validity and thereby validity in general is grounded. At the same time, Kilwardby’s work enhanced the conception of the formality of logic, although he thought that only the syllogistic form is a properly logical form. Analysis of John Buridan’s logic shows that he had a generalized conception of logical form that was tightly knit with linguistic form as it is found in mental language, which he took to be a metaphysically natural domain. Unlike Kant and Bolzano, both Kilwardby and Buridan can be viewed as naturalists as concerns the study of formal logic, inasmuch as they thought that logical validity is grounded in facts that their Aristotelian metaphysics would consider natural.

Central topics in medieval logic are here treated in a way that is congenial to the modern reader, without compromising historical reliability. The achievements of medieval logic are made available to a wider philosophical public then the medievalists themselves. The three genres of logica moderna arising in a later Middle Ages are covered: obligations, insolubles and consequences - the first time these have been treated in such a unified way. The articles on obligations look at the role of logical consistence in medieval disputation techniques. Those on insolubles concentrate on medieval solutions to the Liar Paradox. There is also a systematic account of how medieval authors described the logical content of an inference, and how they thought that the validity of an inference could be guaranteed.

Finland is internationally known as one of the leading centers of twentieth century analytic philosophy. This volume offers for the first time an overall survey of the Finnish analytic school. The rise of this trend is illustrated by original articles of Edward Westermarck, Eino Kaila, Georg Henrik von Wright, and Jaakko Hintikka. Contributions of Finnish philosophers are then systematically discussed in the fields of logic, philosophy of language, philosophy of science, history of philosophy, ethics and social philosophy. Metaphilosophical reflections on the nature of philosophy are highlighted by the Finnish dialogue between analytic philosophy, phenomenology, pragmatism, and critical theory.

The paper considers two kinds of medieval obligational disputations and the medieval genre of sophismata in relation to the kinds of inferences accepted in them. The main texts discussed are the anonymous Obligationes parisienses from the early 13th century and Richard Kilvington’s Sophismata from the early 14th century. Four different kinds of warranted transition from an antecedent to a consequent become apparent in the medieval discussions: the strong logical validity of basic propositional logic, analytic validity based on conceptual containment, merely semantic impossibility of the antecedent being true without the consequent, and intuitively true counterfactual conditionals. As these different kinds of consequences are spelled out by means of obligational disputations, it appears that the genre of obligations is indeed useful for the “knowledge of consequences,” as the anonymous Obligationes parisienses claims.

In this paper, Ockham's theory of an ideal language of thought is used to illuminate problems of interpretation of his theory of truth. The twentieth century idea of logical form is used for finding out what kinds of atomic sentences there are in OckhamÕs mental language. It turns out that not only the theory of modes of supposition, but also the theory of supposition in general is insufficient as a full theory of truth. Rather, the theory of supposition is a theory of reference, which can help in the determination of truth values within the scope of simple predications. Outside this area, there are interesting types of sentences, whose truth does not depend on whether the terms supposit for the same things or not for the same things.