existentialia

is a term referring to the ontological characteristics of Dasein as a ‘who’ whose Being is existence.

Dasein is a "who" whose Being is "existence" and whose ontological characteristics Heidegger dubs existentialia (Stambaugh: "existentials") (67 /42, 70-71/44-5).

is the various dimensions of one’s existence as an entity who has to decide who she is (possibilities, alternatives, etc.).

This means that we will never understand human beings adequately if we treat them as things. Rather than looking at the geologist in terms of quality and quantity, we should look at her in terms of her existentialia - the various dimensions of her existence as an entity who has to decide who she is. These would include her having possibilities, her being confronted with the alternatives of authenticity and inauthenticity, the "mineness" of her Being, and much more.

existentialia, n.All

existentialia