Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā (980-1037) has been christened Avicenna by Latin writers in the European Middle Ages. That fact alone should give an idea of the extent of his reach and his enormous influence world wide. His most famous work, Kitab Al-Shifaʾ (The Book of Healing), systematically discusses the healing of the soul via scientific knowledge. If we focus on his role in the Islamic philosophical tradition, ibn Sīnā can be credited for his synthesis of Kalām and falsafa. He has been called the greatest philosopher in the East[1]. Though he, too, wasn’t always appreciated by his contemporaries (he is assumed to have been quite a difficult if not impossible character during his lifetime and he most certainly did not live an ordinary life as a scholar – he died of sex related illness and was an open alcoholic[2]), his books have been preserved and passed on to later generations, so we can still avail ourselves of a vast corpus by his hand.

Ibn Sīnā’s works can be divided into categories of style: his technical or philosophical writings, his symbolic or poetic writings, and his indicative writings. To focus on what makes him important (if not definitive) for Islamic thought, let’s outline his thoughts brought forth in his technical or philosophical works. In my opinion, a discussion that takes his logic as basis does more justice to his systematic work as a whole, and I will therefore not follow Robert Wisnovsky’s article Avicenna and the Avicennian Tradition[3]. Wisnovsky does point out that ibn Sīnā, as has previously been mentioned, unites Kalām and falsafa; however, he fails to mention that ibn Sīnā does so not only in his metaphysics, but also in his logic. Ibn Sīnā’s logic and metaphysics can be viewed as complementary.

Logic and Metaphysics
Being much more than a mere follower of al-Fārābī, ibn Sīnā logical work differs from al-Fārābī’s logical thoughts in several ways. For instance, unlike al-Fārābī, ibn Sīnā sees logic not as mere method or instrument to acquire knowledge. According to him, it is part of philosophy and has its own worthy subject: the universal concepts and their attributes insofar as they can be part of our knowledge. Also unlike al-Fārābī, ibn Sīnā does allow stoic proposition logic and hypothetic syllogisms, which makes his logic more accessible and acceptable for mutakallimiin (scholars of the Kalām tradition).

Using hypothetic syllogisms, Ibn Sīnā allows for cause and effect reasoning in logic and thereby in his philosophy. He even applies this in his proof for the existence of God. By making the distinction between contingent and necessary existence, he is able to define the relationship between God and the world in terms of cause and effect. His reasoning is as follows: everything in the world exists contingently, since the world could just as easily not exist. What exists contingently needs an external cause. If that cause were to be existing contingently itself, it would also need an external cause and that would result in a chain of effects. That chain could not be infinite without a first necessary cause; otherwise, there would be no actualization of the chain itself. QED: there must be a necessary existing being that causes everything else. In his metaphysics, ibn Sīnā takes his logical proof for the existence of God together with the Neo-Platonic emanation scheme – a perfect match which is very much appreciated by the Kalām tradition.

Ibn Sīnā’s Intuition
Another part of ibn Sīnā’s theory that could be incorporated by the mutakallimiin is his theory on intuition (hads). He uses logical terms to describe its function as the ability to grasp true knowledge. He even considers intuition the highest ability of our reason: all other knowledge we acquire requires our will. Intuition comes in various degrees of strength. Prophets have the highest form of intuition, because they are in possession of the holy intellect of the human soul. In this way, ibn Sīnā is able to not only please theologians by making prophecy and revelation the highest forms of knowledge; as a secondary consequence, his theory of intuition can also be seen as an argument for the theoretical value of allegorical and indicative works – which, as mentioned above, he happened to write as well.