Abstract

This article aims to unravel the doctrine of the “sign from the manifest to the hidden” of Abū Hāšim al-Ğubbāʾī. It shows that Abū Hāšim tended to interpret this sign as an inference, of which he recognized two main types: Type-1 proceeds by analytical deduction of concepts by neutralizing the conditions of their realization, i. e. their ontological basis. This is, typically, the procedure most directly consonant with Abū Hāšim's modal ontology. Type-2 exhibits the same causal relationship at the known and unknown levels and considers causality at the known level to be itself the cause of causality at the unknown level. This partition was completely new in philosophy and kalām at the time of Abū Hāšim, but it is foreshadowed in al-Ḫwārizmī’s Algebra. In this book, al-Ḫwārizmī distinguishes between proof “by cause”, which consists in transferring a certain geometric deduction to algebra, and proof “by expression”, which operates directly on algebraic expressions, which it reduces analytically. A text by Abū Hāšim devoted to human knowledge that seems to refer to the work of al-Ḫwārizmī suggests, finally, that the close parallel between al-Ḫwārizmī’s doctrine of proof and Abū Hāšim's doctrine of the sign may not be a mere coincidence. Two appendices have been added. The first deals with al-Fārābī’s reading of Abū Hāšim's theory of inference. The second, based on all available data, establishes for the first time the correct and precise dates of Abū Hāšim's life.