The interpretation of ‘something being in something’ : the case of Alexander of Aphrodisias

This paper investigates the ontological significance of the apparently simple claim that “something is in something,” arguing that Alexander of Aphrodisias transforms this formula into a systematic problem concerning the mode of immanence proper to form. By tracing this problem through Alexander’s theory of the soul, his interpretation of Aristotle’s Categories, and his engagement with Aristotle’s treatment of differentia, the study clarifies both the unresolved tensions in Aristotle’s own account and Alexander’s original response to them. The first part analyzes Alexander’s account of the soul in De Anima. Against interpretations that construe the soul’s presence in the body either as accidental inherence or as physical containment, Alexander distinguishes several senses of “being in” and identifies the soul’s presence specifically with the way in which form is in matter. This hylomorphic reading enables him to reject the position of Boethus of Sidon, who assimilated form to accidents and subordinated it ontologically to individual substrates. The second part examines Alexander’s engagement with Aristotle’s Categories, focusing on the distinction between what is “said of a subject” and what is “in a subject.” By reinterpreting the notion of being “in” as a part, Alexander resists readings that treat form as an accident and instead articulates a non-accidental mode of immanence that integrates logical distinctions into an ontological framework. The third part turns to Aristotle’s own treatment of differentia and brings into focus a fundamental ambiguity left unresolved in his account. While Aristotle classifies differentia as something that is “said of a subject but not in a subject,” he offers no systematic explanation of how differentia is related to essence or how it operates within the hylomorphic structure of substance. This lacuna becomes especially problematic once differentia is required to function as a principle of essential determination in definition. The final part shows how Alexander addresses this unresolved problem in his Reports of the Keio Institute of Cultural and Linguistic Studies 57 (2026), 113-130 treatise De Differentiis. Rejecting both the view that differentia belongs to a genus as one of its species and the view that it is an independent universal form, Alexander characterizes differentia as “form without matter” that nevertheless operates within material forms. On this basis, the paper concludes that the soul itself must be understood as a structured unity of such differentiating principles. By redefining immanence in this way, Alexander secures an intermediate ontological domain that avoids both reduction to individual substrates and appeal to transcendent Platonic Forms, thereby unifying logic, natural philosophy, and metaphysics.