Two words to keep apart: _Seiendes_ means a being or entity; _Sein_ concerns what it means for that entity to be. This is the ontological difference. Dasein is an entity whose own being matters to it ([Stanford Encyclopedia of Philosophy, §2.1](https://plato.stanford.edu/entries/heidegger/#KindBein)).Being that in its Being is concerned about its very Being.
The word _Dasein_ joins _da_ (there) and _sein_ (to be), literally “being-there” ([translators’ note, p.27](https://libraryofagartha.com/Philosophy/Martin%20Heidegger/Being%20and%20Time%20%28Martin%20Heidegger_Berserker%20Books%29.pdf)). Situated-ness means that our lives already involve tasks, other people, and shared practices through which things matter to us. Heidegger calls this being-in-the-world. Even asking who I am starts from this involvement ([§12](https://www.beyng.is/pages/en/BeingandTimeMR/BeingandTimeMR.078.html)). ### tenet Two characteristics of Dasein: 1. Dasein exists: “The essence of Dasein lies in its existence” (p.42). 2. Dasein is mine: “the Being, whose analysis our task is, is always mine” (p.42). Existence here includes the possibilities through which someone lives: what they pursue, avoid, or leave open. Mineness means those possibilities concern someone’s own life ([Stanford Encyclopedia of Philosophy, §2.1.3](https://plato.stanford.edu/entries/heidegger/#Dase)). ### context A hammer’s use involves nails, materials, and something being built. In hammering, attention usually goes to the work. Heidegger calls this way of encountering equipment _readiness-to-hand_: the hammer is understood through using it within a task ([§15](https://www.beyng.com/pages/en/BeingandTimeMR/BeingandTimeMR.098.html)). Measuring its weight or inspecting its material properties brings a different aspect into view, which Heidegger calls _presence-at-hand_. The distinction concerns how equipment is encountered. Calling the hammer “for hammering” leaves the wider task unexplained; the relations among tool, materials, and purpose supply that context ([Stanford Encyclopedia of Philosophy, §§2.1.1–2.1.2](https://plato.stanford.edu/entries/heidegger/#OccuPresHand)).In the Being (Sein, ontological) of this being (Seiendes, ontical) it is related to its Being (Sein, ontological).