A reference to al-Fārābī’s Kitāb al-Ḥurūf in Averroes’ critique of Avicenna (Tahāfut al-Tahāfut, 371,5-372,12 Bouyges).

Al-Fārābī’s Book of Letters (Kitāb al-Ḥurūf) and the analyses devoted in this text to the terminology of ‘Being’ are authoritative references for Averroes from the epitomes of his youth to his mature treatises. Also the Farabian doctrine of the conventionality of the natural language plays a role in Averroes' thought. This paper discusses the Tahāfut al-Tahāfut, 371.5-372.12 Bouyges, where Averroes has recourse to the Book of Letters in criticizing Avicenna’s distinction between essence and existence. Averroes explicitly mentions the title of the work and recalls a passage from the fifteenth chapter. This passage had already inspired him in the Epitome on Metaphysics, where Averroes did not mention explicitly his source, but followed in al-Fārābī's footsteps as for the analysis of the uses of ‘being’. This was one of the points in Averroes' critique against Avicenna. Averroes uses tacitly the same passage also in his Commentary on Metaphysics Delta 7.