Translated by Pete Ferreira
As to the meaning of substance, the meaning traditionally considered as fundamental and also regarded as so by Brentano, it can be assumed that Heidegger convinces himself right away of its inadequacy to enact the fundamental meaning of being, given that, beyond giving an account of all of its senses, he restricts them to the metaphysical-scholastic horizon of presence and of θεωρία. Here, against the reduction of ontology to ousiology, Heidegger notes: "Already in the Middle Ages, on the basis of the above sentence from the beginning of Met. Θ 1, it was concluded that the first guiding fundamental meaning of being in general–for the four ways together as well. not only for the one and its multiplicity–was οὐσία, which is usually translated as 'substance.' As if being possible and actual and true also had to be led back to being in the sense of substance. They were even more inclined to conclude this in the nineteenth century (especially Brentano), since in the meantime, being, being possible, and being actual had come to be perceived as categories. Hence it is a generally accepted opinion that the Aristotelian doctrine of being is a 'substance doctrine.' This is an error, in part resulting from the inadequate interpretation of the πολλαχῶς; more precisely: it was overlooked that only a question is here first of all being prepared. (W. Jaeger's reconstruction of Aristotle is built upon the basis of this fundamental error.)"48
As for the meaning of being as truth, as we have seen in the 1920s, Heidegger thoroughly validated the ontological scope, returning to it several times on the problem and the discussion of it given by Aristotle. We have seen then how Heidegger distinguished truth, as the character of the happening of being itself, from the being-true that distinguishes the discovering attitude of being-there when it is co-originator in relation to the entity that manifests. We have seen as well how through this interpretation Heidegger develops his conviction that the Greek understanding of being was closely linked to the idea of constant presence (which would have prevented the explicit thematization of the whole temporal extent of being).
Here, finally, in 1931's lecture course, Heidegger achieves the breakthrough which – together with his thorough confrontation with the Presocratics, Nietzsche and Hölderlin, and along with reading of Ernst Jünger – profoundly affects the development of his philosophical perspective and his critical-assimilative disposition towards Aristotle: we mean the discovery, or better, the emergence in a decisive way of the meaning of being as ἐνέργεια, which not only provides Heidegger with a decisive means to understand the unity of being, but also refers to that un-thought of metaphysics, that precedes and conditions it as a remote possibility; it is the source meaning, the total and originary meaning of being as φύσις.49
48 GA 33, 45-46. [Aristotle's Metaphysics Theta 1-3 On the Essence and Actuality of Force, 37.]
49 An initial discussion of the Aristotelian concept of φύσις, that preludes the theses revealed in the celebrated 1939 essay (1958), is located at the beginning of the winter semester course 1929/30 in the context of a discussion of the meaning of the term meta-physics (GA 29/30 [The Fundamental Concepts of Metaphysics.], § 8 d). The importance of Aristotle in Heidegger's way of thinking has been highlighted in numerous studies from Thomas Sheehan, in particular in "On the Way to Ereignis: Heidegger’s Interpretation of Φύσις", in Continental Philosophy in America, ed. by H. J. Silverman, J. Sallis, Th. M. Seebohm, Duquesne University Press, Pittsburg 1983, pp. 131-164.