(The "Being and Time" class filled up in the first three hours of registration today. Hopefully somebody drops, or that I just end up being so gosh darn endearing he overrides the registration cap. Thus the conditional in the title.)
From "Truth and Finitude" part II, p.5 in the PDF. Haugeland is describing two "popular conceptions" of death, to which Heidegger opposes the existential sense of "death":
The first of these he calls perishing. This is the ubiquitous and all-too-familiar biological phenomenon that is the cessation of systematic biological function in an organism (and, typically, the onset of organic decay). All organisms eventually perish: plants, animals, fungi, and what have you, including all specimens of Homo sapiens. But Dasein never perishes -- not because it is immortal or everlasting, but because it is not a living organism in the biological sense at all.
The second popular conception of death Heidegger calls demise. Unlike perishing, demise is not a biological phenomenon, but pertains exclusively to Dasein. It is instead a social-cultural phenomenon. Roughly speaking, demise is that social event upon which you cease to be countable in the census, your spouse becomes a widow or widower [etc]. Although demise typically coincides with the perishing of an organism, these are not at all the same. The relationship between demise and perishing is loosely analogous to that between marriage and mating (which likewise are not at all the same).
Is the reason Dasein never "perishes" just because Dasein is a class noun -- i.e., does Dasein-in-each-case perish? If so, then why didn't Haugeland just say that? Or is Dasein-in-each-case supposed to be distinct from a specimen of Homo sapiens sapiens (which would be weird)? What are "specimens of Homo sapiens" if examples of Dasein-in-each-case are not? Pre-linguistic infants, I guess?
Since "all specimens of Homo sapiens" perish, I feel compelled to infer that the reason Dasein never perishes is because Dasein-in-each-case is the thing that perishes (as a specimen of Homo sapiens). But that doesn't seem to be what Haugeland meant. If it were, it'd be clearer to just note the Dasein/Dasein-in-each-case distinction, rather than just say that Dasein is "not immortal or everlasting". Hmm. Maybe I'm just reading too much into it.
The existential sense of "death" is the only one that's said to "individuate" Dasein. That much is clear. But it seems that non-individuated (fallen) Dasein can suffer "demise" but not "perish". But then what's the "specimens of Homo sapiens" doing there? (It also makes me wonder how far we're supposed to be able to take the analogy with mating and marriage. It strikes me as reasonable to say that human beings don't "mate" -- mating is a bestial behavior, to put it pointedly. So, by analogy, human beings wouldn't "perish" -- we don't die in the way that animals and fungi and plants die. But Haugeland explicitly says that "specimens of Homo sapiens" perish just like animals and plants and fungi.) Frown. I am puzzled.
Unrelated note that didn't deserve its own post: I read the introduction to Hegel's Philosophy of Nature the other day. It was a lot better than I expected. Hegel's goal in the Naturphilosophie is to reconcile the "practical approach" taken in everyday life with the "theoretical" point of view typical of the natural sciences. It seems clear in retrospect that his attempt did not work out. But, that's clearly a reasonable thing to want to try to do. It also explains a reference I once saw to McDowell as a Naturphilosopher.