In search of lost substance. Brentano on Aristotle’s doctrine of categories

Brentano’s doctoral dissertation 'On the Manifold Senses of Being in Aristotle' (1862) takes up Aristotle’s ontology and theory of categories in order to show that a realistic ontology requires the interweaving of factual being and its adequate logical expression. The scheme of categories manifests itself on a grammatical-linguistic level – as Trendelenburg pointed out – , but it is grounded in the variety and multiplicity characterising the level of real things – as Aquinas held. The logic-linguistic side of the categories is thus dependent on the ontological and founded by it. Brentano’s first book thus has two main interpretative sources, one which is fundamental but hidden, the other more explicit but superficial: the first is Thomas Aquinas – for Brentano as a young catholic seminarian, of course, 'sine Thomas mutus esset Aristoteles' – , the second Adolf Friedrich Trendelenburg, his Berlin teacher and leader of the Aristotelian revival in Protestant Germany. The Thomist influence lead Brentano to propose a univocal reading of the Aristotelian ontology, allowing that deduction of the categories from the general concept of being, that Aquinas had already worked out during the Middle Ages. Considering the Aristotelian ontological framework compatible with a deductive trend, which was aimed at bringing the equivocal nature of being back to an analogical structure, Brentano forced, at least partially, an interpretation that would be particularly appreciated by Heidegger, to the point that according to him it is due to Brentano that “the systematic impact of Aristotelian philosophy begins”. This Thomist influence is also analysed through a comparison between the printed version of the dissertation and its preliminary version, dating back to 1861, which is preserved as a manuscript in Brentano’s Nachlass (Werkmanuskripte, Frühe Schriften, Ms. 16)