i agree that the glass is not so significant in this question. the answer, i believe, is all in the eyes of the beholder. one may see the glass half empty, but another may see the glass as half full from their own, completely unique perspective. let us consider the liquid in the glass water, the plainest of liquids. in my perspective, i consider the glass both half empty and half full of water. but, here on earth, unless in a controlled environment, the glass would have to contain air in the space that is not occupied with the water. but, half full (or empty) in one glass will inevitably take up a different amount of space in most other glasses. the question is how many milliliters/ounces/whatever measurement you wish to use. so, the question does not need to be asked in the practical sense, but rather is just a philosophical question that cannot be answered because of our concepts of empty and full that was fabricated by people like us who want to confuse others.