This questioned can be answered in a number of different way's. The most common time that this phrase is used is when someone is talking about life and if your live is half full (which means you consider yourself to be a good being of life and satisfied with yourself) or half emtpy (which means you are asking yourself if you think you have done somthing with your life and if it is missing somthing). Another way is just saying that you have just drank somthing and it is half empty or you just filled it up and its half full.
The question is an expression to see if the person who answers it is either optimistic, or pessimistic. If the person answers "half full", it means that he/she is optimistic, meaning that he/she expects the good things to happen in the future. If he/she answers "half empty" instead, that person is pessimistic, meaning that he/she expects the bad and terrible things to happen in the future. Thanatochronic (talk) 21:12, October 26, 2013 (UTC)