Translated by Pete Ferreira
From this perspective, characterized by the contrast between the theoretico-Husserlian determination of the subject and the productive appropriation of Aristotelian determinations, one must read and understand the analysis of the modes of being of human life that Heidegger elaborates in the Marburg courses and exposes in completed form in the existential analytic of Being and Time. Then one can understand how the main determinations of existence come to be made by Heidegger by means of re-purposing and radicalizing the determination of human life already conceived and elaborated by Aristotle.
Now, to the exclusion of all other aspects of the analytic of being presented in Being and Time, one can say that from an ontological point of view it should introduce the distinction of three fundamental modes of being, namely existence (Dasein), usability (Zuhandenheit) and simple presence (Vorhandenheit). As is well known, existence – connoted as a being-in-the-world opened up in confronting the entity and characterized in this opening (Erschlossenheit) by certain structures called 'existentiale' – is the proper way of being of human life. As such existence is radically distinct from the way of being of entities different from it (nichtdaseinsmäßiges Seiendes), that is, from the way of being of 'things'. These, depending on the disposition in which the being-there finds itself, may be encountered in the way of either usability (when they are used as instruments or tools in an operations environment) or as simply present (when they are the subject of mere observation).
With all the caution that such a comparison imposes, it is reasonable to see a correspondence, not only formal, between the Heideggerian distinction of these three modes of being (Dasein, Zuhandenheit, Vorhandenheit) and the Aristotelian determination of πρᾶξις, θεωρία and ποίησις (which, as has been seen, Heidegger interprets as ways of the being-discovering of the being-there in relation to the entity). The assertion of this correspondence however requires a justification. Because, while the parallel between ποίησις and Zuhandenheit and between θεωρία and Vorhandenheit is self-evident, the correspondence between πρᾶξις and Dasein is not entirely clear. Indeed, when considered in the light of contemporary interpretations of the analytic of being, this correspondence looks totally uncharacteristic. Let's try, then, to attempt an explanation.