Ibn Sina (Avicenna) was certainly one of the most important logicians of the Aristotelian tradition between Aristotle himself and the late nineteenth century. But information about his logic is still hard to come by. This makes the new English translation by Asad Q. Ahmed of the logic section of Ibn Sina’s Deliverance (Najat) a major event in Arabic logic. Ahmed provides a full translation with explanatory notes and a glossary. There is a short but informative Introduction by Tony Street. One thing missing is an explanation of the name of the book: Ibn Sina says in his introduction that the book was written to help the reader to ‘achieve deliverance from drowning in a sea of misinformation’.
All the works of Ibn Sina on logic that have been published in modern times are first sections of general treatises on philosophy. Ibn Sina took the view that we need a good grasp of logic before we can think usefully about anything else. According to the generally accepted dating, he wrote all but one of these works in his forties or fifties.1 The exception is the logic of the Deliverance, which he wrote at the age of about thirty-three but published more than a dozen years later. Earlier logical works of his are known, but in modern times they have barely been studied, let alone published. The published works differ a good deal in style and length, but they present broadly similar accounts of logic; often we can use one of the texts to clear up obscurities in another. The account in the Deliverance is perhaps the most straightforward. It presents Ibn Sina’s own thoughts first on meanings and sentences (corresponding to Aristotle’s De Interpretatione), then on syllogisms (corresponding to the Prior Analytics), and finally on knowledge and science (corresponding to the Posterior Analytics). [End Page 224]
1. A short guided tour
Paradoxically, it’s clear that Ibn Sina was a highly original thinker, but it is much less clear what his originality consisted in. Different readers of Ibn Sina will give you different views on this. Ahmed’s translation could help you form your own opinion. To read through from pages 1 to 148 is tough, but I would recommend dipping in at various points and looking for the interconnections. For example, here is a short guided walk.
Start at section 134, whose first sentence (page 110) reads:
Demonstration supplies perpetual certainty, [but] nothing holds perpetually of things that are corruptible.
For example, human bodies are corruptible, so there can be no demonstration of facts about human bodies. The point is startling when we note that this same Ibn Sina wrote the Qanun, the great medical textbook that served as gospel for European doctors until the Renaissance. How could Ibn Sina be a leading spokesman for medical science on one day, and deny its existence on the next? In fact two pages later in the Deliverance you will find an example of a medical syllogism. So the contradiction is stark.
Much of Ibn Sina’s logical work can be seen as an attempt to resolve this contradiction. If we can prove a proposition, then the proposition must be ‘always and necessarily true’. But there are several ways of being ‘always true’ that can apply to corruptible objects. Ibn Sina introduces some examples in his section 48 (page 28). For example every human is an animal for as long as he exists. Everything white is coloured as long as it stays white. The moon is eclipsed whenever the earth comes between it and the sun.
Aristotle’s logic had little or nothing to say about sentences like these. They are like the sentences of Aristotle’s logic except that they also include ‘conditions’ or ‘additions’ (two very common words in Ibn Sina’s logic; see Ahmed’s note xlii). So one task for logicians is to rework Aristotle’s system of logical rules – conversion rules and syllogisms...