Brendan Mahoney on the infinitive in there being.

Da-sein consists of two parts: the adverb “Da” (here/there) and the infinitive “sein” (to be). Instead of adopting the view of the “present day grammarians [who] say that the infinitive is the ‘abstract verbal concept’” (IM, 67), I think it is fruitful to follow a hint in Heidegger’s Introduction to Metaphysics: “The infinitive no longer manifests what the verb otherwise reveals” (IM, 68). The emphasis falls on “no longer,” which implies that ‘at one time’, the infinitive revealed something other about the verb than the “abstract verbal concept.” Perhaps what the infinitive no longer manifests is “the fact that it names something which underlies all the inflections of the verb” (IM, 68). The key to unpacking this statement is the concept of inflection, which the Greeks called enklisis. Heidegger writes, “the infinitive … is a special mode of the verb, an enklisis” (IM, 65). As inflected, “what is named in the word is not invoked as really present but represented as only potentially in being” (IM, 65). He further explicates enklisis as follows: “To disclose something different along with the fundamental meaning, to cause to arise and be seen: therein lies the power of the enklisis, in which the erect word leans to one side” (IM, 65). The erect word––that which appears, stands up/out, i.e., the infinitive––leans to one side––i.e., withdraws, conceals and shelters itself––so that what is inflected (mood, person, number) can appear.

Heidegger specifies this understanding of enklisis as enklisis paremphatikos. I think it is significance that when clarifying paremphaino, he employs, in reference to Plato’s Timaeus, the Greek concept of chora. At the end of a parenthetical aside concerning the roots of the modern conception of space as extension in the Timaeus, he poses a curious question: “Might chora not mean: that which abstracts itself from every particular, that which withdraws, and in such a way precisely admits and ‘makes’ place for something else?” (IM, 66). I want to follow the path of this thought and return to the infinitive. The infinitive is an inflection (enklisis) of the verb, and as enklisis––whose meaning we can enrich by drawing from the concept of chora––it makes a place for particular moods, persons and numbers to emerge by ‘leaning to the side’, i.e., withdrawing itself. Perhaps the infinitive grounds all the other verbal inflections precisely because it does not appear as a particular inflection. This withdrawal makes a space within which and out of the specific inflections emerge; thus, the present day grammarians only see it as an ‘abstract verbal concept’ because they focus solely on the particular moods, tenses, numbers and persons, and in so doing, have forgotten the significance of the infinitive as ‘leaning to the side’.

From "Da-sein’s Earthly Body: Ethos as Eco-logic".  ¶ 3:44 AM