To delineate a particular, arbitrary edge of a glass is to simply prefer one boundary over another. Who, for example, ever fills a glass so close the edge that the only thing keeping it from overflowing is an undisturbed surface tension? No one!
That leads to my first question:
Is that the only inarguable condition of a true fullness?
Here, we see a glass, having a finite, upper boundary, as all glasses do, with respect to an accelerated frame of reference within a gravity well shared by all participants. It contains some substance not part of the glass, held by the walls of glass, but not combined with the glass, separated as the water is from the glass because of the weakness of intermolecular attraction.
That might pass as an abbreviated physical description. It does not bring us much closer to any kind of satisfying answer. A problem of determining a halfway point is not immediately obvious, even when considering our introductory question.
After all, it seems obvious that there is some place in the glass equally distant from the top and from the bottom. We could choose from at least two methods of determining a “halfway” point that would satisfy certain kinds of problems: We could measure an equal distance along a line from the top and bottom or measure the entire volume of the glass and halve it, noting in either case, whether the fill-point corresponds to either of the two schemes.
But these schemes avoid the more insidious problem; they simply take as granted (among other things) that true “fullness” is something quite different than the “fullness” we expect and use in practice!
This leads us directly into a tension between what we know or suspect to be true and what we are able to negotiate socially. The idea of what a full glass looks like is at least as dependent upon social and psychological factors — I would argue, more so — than just the raw “physics” of the glass! I would submit to you that if you were a guest at my home or pub and I filled a glass to the top, in a manner conforming to a strict definition of “full”, straight to the top to the point of spilling everywhere (if not actually spilling!), you’d think me odd, perhaps even rude. “I can’t walk around with the glass this full!”
The expression,”this full” reveals an expectation and describes a type or species of “full”. Contingent. Relative. Not absolute. Isn’t that a little strange? Isn’t “full” in fact an absolute condition? How can we have different kinds of full? Well, I think these are the contingencies of ideological conditioning; the presumptions we make in order to function socially. [Did you know that you knew that already?]
We might continue in this way, exploring the boundaries of the meaning of words and asking questions forced upon us reflexively by virtue of our own invasive curiosity. But “space is limited” and “time is short”; people want answers; we have to “wrap it up”. We come at last to the point where we have to ask, “Is the glass half full or half empty?”; and we can see now, already, that the question is too simple!
Before we answer that question, we have to ask what it means to be “full”! What are the expectations? What are the limitations? How does the horizon of our own ideological assumption force us to ask questions seeming only to give us the answers we want?