In 2003 Zia Movahed pointed to a passage of Avicenna, written probably in 1022, which Movahed claimed anticipated the modal formula of Barcan (that ‘For every |$x$| necessarily |$\phi $|’ entails ‘Necessarily for every |$x$||$\phi $|’), and its converse. Since 2003, examination of early logical writings of Avicenna has clarified how he understood entailments between modal sentences, using his own new temporal language to provide a kind of semantics. In the light of that, Movahed’s claim for the Barcan formula needs (...) some tidying up but is basically correct. But by his semantics Avicenna should not have claimed the converse Barcan formula and probably didn’t claim it. (shrink)

We record the advances made by the eleventh century Persian logician Ibn Sina—known in the West as Avicenna—away from a purely cognitive view of proofs and towards a more computational view, and the kinds of consideration that led him to these advances. Some of Ibn Sina’s new logics, which stand somewhere between Aristotle’s categorical syllogisms and modern first-order logic, can serve as a kind of laboratory for testing what are the differences between Aristotelian and modern logic, and where these differences (...) come from. (shrink)

In this article, I discuss Robert Kilwardby’s theory of judgement and consider its implications for his view of truth and falsity. I start by considering Kilwardby’s claim that truth and falsity are primarily found in composite thought, i.e. judgement. I then examine his distinction between two different kinds of being, namely real and conceptual, arguing that different kinds of true judgement, according to Kilwardby, have different kinds of existential import, either real or merely conceptual. Since Kilwardby develops his position by (...) commenting on Aristotle’s logical treatises, an important aim of the article is that of showing how he addresses exegetical issues in those sources and offers solutions that go beyond Aristotle’s alleged intentions. The focus of the paper is on negative judgement because that is where Kilwardby diverges from Aristotle most conspicuously. (shrink)

Appealing to some analytic tools developed by contemporary analytic philosophers, I discuss Avicenna’s views regarding the problem(s) of linguistic and mental reference to non-existents, also known as the problem(s) of ‘empty intentionality’. I argue that, according to Avicenna, being in an intentional state directed towards an existing thing involves three elements: (1) an indirect relation to that thing, (2) a direct relation to a mental representation of that thing, and (3) a direct relation to the essence of that thing. Empty (...) intentionality does not involve the first element. Moreover, depending on the nature of the non-existent we are thinking about, the third element may not be involved either. Thus, the necessary element of being in an intentional state towards something is to be related to a mental representation of that thing. The nature of this representation may vary depending on the nature of the non-existent towards which our thought is directed. (shrink)

The square of opposition has never been drawn by classical Arabic logicians, such as al-Fārābī and Avicenna. However, in some later writings, we do find squares, which their authors call rather ‘tables’ (sing. _lawḥ_). These authors are Shihāb al-Dīn al-Suhrawardī and Muhammed b. Yūsuf al-Sanūsī. They do not pertain to the same geographic area, but they both provide squares of opposition. The aim of this paper is to analyse these two squares, to compare them with each other and with the (...) traditional square of opposition drawn by Apuleius and Boethius, with regard to their particular structure and their vertices and to evaluate their validity. We will show that both squares are different from each other and from the traditional square both with regard to their vertices, and to the arrangements of the oppositional relations. In addition, while al-Suhrawardī uses the notion of matter modalities to define the oppositions, al-Sanūsī relies rather on al-Rāzī’s and al-Khūnajī’s distinctions. Both authors agree, however, on the fact that affirmatives have an import while negatives do not. For this reason, their squares are valid from a logical viewpoint. As diagrams, these squares are nevertheless entirely original, due to the particular arrangements of their oppositional relations. Our analysis shows also that the later author does not seem to know the square drawn by the earlier one and that both authors do not seem to know Apuleius’ or Boethius’ squares. (shrink)

This paper explores a neglected category of propositions in Arabic logic, propositions with negative predicates (sālibat al-maḥmūl), by addressing two pivotal questions concerning this propositional form: first, whether it is possible to defend it as distinct from metathetic and simple negative propositions and second, whether affirmative instances of these propositions have existential import. The paper argues for the existence of two distinct and conflicting theories of existential import frequently implicit in the views of Arabic logicians: one centered on the copula (...) and the other on the predicate. (shrink)

The aim of this paper is to analyse categorical propositions and their oppositional relations in Avicenna’s frame. For Avicenna’s expression and conception of categorical propositions is different from those of the authors who preceded him, due to the various conditions he adds to these categorical propositions. These additions make the oppositional relations richer and give rise to many more figures than a simple square. Our analysis exhibits some of these figures by relating all kinds of quantified propositions in various ways. (...) We thus find many squares of oppositions, several octagons, two hexagons and many complex figures which are different from each other and have specific and original structures, due to the propositions they contain. The hexagons are of Blanché’s kind, but one of them is asymmetric. Some octagons are of Buridan’s kind, but one of them is very unusual and seems to be a reversal of Buridan’s octagon. These octagons can also be replaced by cubes, which are three dimensional figures having the same number of vertices. (shrink)

In this article, I discuss Robert Kilwardby’s theory of judgement and consider its implications for his view of truth and falsity. I start by considering Kilwardby’s claim that truth and falsity are primarily found in composite thought, i.e. judgement. I then examine his distinction between two different kinds of being, namely real and conceptual, arguing that different kinds of true judgement, according to Kilwardby, have different kinds of existential import, either real or merely conceptual. Since Kilwardby develops his position by (...) commenting on Aristotle’s logical treatises, an important aim of the article is that of showing how he addresses exegetical issues in those sources and offers solutions that go beyond Aristotle’s alleged intentions. The focus of the paper is on negative judgement because that is where Kilwardby diverges from Aristotle most conspicuously. (shrink)