Between Matter and Form: Complexion (mizāǧ) as a Keystone of Avicenna’s Scientific Project

According to Avicenna, the perfect (or complete) disposition (istiʿdād kāmil/tāmm) turns prime matter, which is potentially receptive to every form (or power, or quality), into complected matter, which is endowed with uniform quality. The latter, i.e., complexion (mizāǧ) or complexional form (ṣūra mizāǧiyya), is suitable to receive some particular form (or power, or quality) and not another. The question arises as to how matter acquires its specific complexion. Is it the result of celestial influence, or does it emerge from chemical, elemental interactions within matter? This paper tries to answer this question with textual evidence from Avicenna’s natural philosophy and metaphysics. Together with soul/form, complected matter represents the other constituent of organic, living substances. The paper then attempts to determine which science is proper to its investigation. I argue that the investigation of organic matter, that is, the specific complexion characterizing the animal body (or its parts), pertains to zoology. Zoology is crucial to grounding medical practice, which operates on those specific complexions to preserve or restore health.