Optimism?

"Do you see this glass as half full, or half empty?" I think that the answer to this question should be. "Neither, 50% of this glass contains water." (I used "inkscape" and "Gimp" to make the awesome graphic, isn't it nice?)

Also, if the "50%" answer is unacceptable, I'd ask about the process that the glass is going through. If the glass is being drained, I'd say that it was half empty. If it was being filled, I'd say that it was half full. I don't know why this seems to make the most sense to me, but it does nonetheless.