How did Heidegger argue for the certainty of death?
I gather that's a component of one characteristic of death, that it's "not to be outstripped". The other component being its indefiniteness, that I don't know when I will die.
I'm not very sympathetic to either claim taken completely literally. While it's not impossible that I'm about to have a massive heart attack (I've just had it checked out etc.) it seems so improbable that I'll die before I finish this question, that it's not very different to saying that my house is about to fall down, and making that some important practical principle. Likewise, it's not obvious that all people certainty die (which cannot be experienced) rather than demise, else most or all religions would be trivially vacuous.
Are these two components of its not being outstripped meant as emotional appeals, or can they really be made sense of, either as non-literal expressions or statements of doubt (in the possibility of an after-life, that I could have died)?
I would often agree that death cannot be actualized, is always not yet, but not because it is certain and indefinite, only because it can't be experienced by who dies.
It is called certain in the sense of "being certain as a kind of being of Dasein". This is the "primordial" sense of certainty. Inauthenticity is it also "certain" of death, but it covers up the "thrownness" (p245 SUNY Press) into death.
Because "thrownness" is how the world matters to me, perhaps he just means that death is "certain" in that it matters (to "hold" it for true) that I will die. Is that how he argues for it? Or does "death" mean something else other than the termination of experience?