Indeterminate Propositions and the Emergence of Truth in the Ikhwān al-Ṣafāʾ’s Theory of Quantifiers ( Sūr )

This article argues that the Ikhwān al-Ṣafāʾ introduce a distinctive technical and normative innovation into tenth-century Islamic logic through their account of sūr: truth and falsity become manifest only when a statement is sufficiently closed against interpretation, by quantificationally bounding the subject in the case of muhmala propositions and by securing reference in the case of makhṣūṣa propositions. Through a close reading of Barāmānīyās and the adjacent logical epistles, the article explicates the Ikhwān al-Ṣafāʾ's twofold diagnosis of unbounded or insufficiently determined speech: muhmala propositions are scope-indeterminate, whereas makhṣūṣa propositions are apparently singular yet referentially unstable. Each blocks stable public assessment by allowing interpretive retreat in disputation. The Ikhwān al-Ṣafāʾ's solution is not merely classificatory: they connect quantificational and referential closure with an ethical directive that hearers bind speakers to what is explicitly said rather than to unverifiable private intentions, thereby turning closure into a mechanism of public accountability. The article then uses contemporary formal notation to distinguish semantic, pragmatic, and inferential closure. Finally, it locates the Ikhwān al-Ṣafāʾ's account historically by contrasting it with Aristotelian practice, al-Fārābī's propaedeutic curriculum, Avicenna's treatment of muhmala, post-Avicennan semantic refinements, and medieval Latin theories of supposition and the properties of terms.