Struggling with the Essentials: A Debate between Avicenna and His Contemporaries on Essentiality and Necessity in Demonstrations

Central to Avicenna’s (Ibn Sīnā, d. 428H/1037) logic are the definitions of essentiality and necessity and the assessment of their roles in demonstrations. Avicenna’s reworking of Aristotelian logic puts particular emphasis on the distinction between essential and accidental, necessary and contingent attributes. Most crucial in this respect is Avicenna’s classification of essential and accidental attributes based on their different degrees of separability from their subjects, namely separability in estimation (tawahhum) and in existence (wuǧūd). This taxonomy addresses interpretative challenges encountered by earlier exegetes, particularly regarding the distinction between essential constituents (ḏātiyya muqawwima) and non-essential implicates (lawāzim). This paper aims to reconstruct the debate between Avicenna and his contemporaries on this subject, drawing from primary sources such as Avicenna’s reworking of the Posterior Analytics (Kitāb al-Burhān) in the Kitāb al-Šifāʾ (chapter II.2) and his Letter addressed to Vizir Abū Saʿd. These writings preserve traces of the elaborations on the subject by the philosophers of the Peripatetic school of Baghdad and by intellectuals more or less directly affiliated with it (including Abū l-Qāsim al-Kirmānī), thus enabling us to reconstruct the fundamental lines of an otherwise lost debate.