My new answer

I saw a t-shirt - at Threadless or somewhere - that said "Technically, the glass is always full" (showing a drinking glass half-filled with water....suggesting the classic question, "Is the glass half full or half empty?")

Because the half of the glass not filled with water is filled with air.

For some reason I find that really amusing and I really like it, and I think I will be thinking it (if not outright saying it) in the future when the question of "glasses half full" comes up. I think I like it because it's a slightly smart-aleck response (Of COURSE a scientist would point out that air is a "thing," so a glass can be full of air), but it also is mildly thinking outside the box (to use a phrase I detest as much as those criticism "sandwiches" I was talking about earlier this month).

One could also see something vaguely Zen (at least, in the sense most of us Westerners interpret "Zen") as the statement, "Technically, the glass is always full." That what some see as "emptiness" is just "fulness" of a different type.

Maybe I'm also seeing it as being a bit in the same spirit as Therese of Lisiuex exclaiming "I choose all!" when presented with a choice of hair ribbons...