In 1931 Heidegger again considers the philosophical significance of ‘dunamis’; this time in the context of the first three chapters of book 9 of Aristotle’s Metaphysics. Here Aristotle presents ‘dunamis’, or potency, in two ways: as a force applied in acting, and as a force received by ‘being acted upon’. In acting it is the potency of something else that is affected, whereas, in ‘being acted upon’ it is one’s own. These are not powers additional to being, but constitute what something is in itself; they are “indissociable from the essence of being”, as Heidegger puts it. However, for Heidegger, the fundamental meaning of potency so far as Dasein is concerned relates to the external expression of ‘dunamis’, i.e., to what it produces through acting. Since, for Heidegger, “all the phenomena found under the title ‘dunamis’” – capability, talent, skill, proficiency, being accomplished etc., are all gathered together in “ability”. As Dasein is the “being on the way towards an accomplishment.” However, all these productive actions relate to ‘kinēsis’, which is not the activity of being. For Aristotle the primary significance of ‘dunamis’ relates to ‘being acting upon’, because what results from ‘being acted upon’ in the way Aristotle describes is a change in the one ‘being acted upon’ to an active condition and into that thing’s nature. It is this notion of ‘dunamis’, i.e., concerned with ‘being acted upon’ by an operative reality that is the more important one for book Θ because this meaning of ‘dunamis’ is concerned with the deep structural features of being. Heidegger sees in ‘producing a work’ a decisive determination of the existential being of Dasein, “a fundamental posture toward the world,” and, by contrast, sees a lack of producing as a ‘failing’ of ‘dunamis’ - a sinking into ‘unforce’. Heidegger regards the other form of potency, i.e., ‘being acted upon’, as synonymous with “impotence” and “deprivation”. Because, for him, the potency that relates to the ‘being-at-work’ of a being relates to what it can bring forth and not to what it can actually be.