Is the glass half empty or half full?

Lately I have been conversing with several people whom I perceive as showing themselves to be, most definitely, either a glass half-full or a glass half-empty personalities. It is amazing to me that even before I ask them a question I know what the answer will be based in this idiom. So, I played with the idea a bit today and found some interesting perspectives.

Is the glass half empty or half full? is a common expression, used rhetorically to indicate that a particular situation could be a cause for optimism (half full) or pessimism (half empty); or as a general litmus test to simply determine if an individual is an optimist or a pessimist. The purpose of the question is to demonstrate that the situation may be seen in different ways depending on one's point of view and that there may be opportunity in the situation as well as trouble.

This idiom is used to explain how people perceive events and objects. Perception is unique to every individual and is simply one's interpretation of reality. The phrase "Is the glass half empty or half full" can be referred to as a philosophical question.

Optimistic: half-full.
Pessimistic: half-empty.
Really Ticked Off: it is empty (I drank it)
The Engineer: it is twice as big as it needs to be.
Neither: It is always full.

It may be filled with 50% of water and 50% of air, or any variation of competing percentages, but it is always full of something even if it looks empty as it could be FULL of air.

That's relative.
It's completely empty until you put something in it.

The cup is half full. A glass can't be half empty because half of nothing is still nothing.

Was the previous condition of the glass full or empty?

If full, then the answer is half empty.

If empty, then it is half full.

It really doesn’t matter does it but if you drank it first its half empty if you filled it up and haven’t drank from it yet its half full that is the logical answer not so difficult.

If you pour water into a cup until its filled half way, the cup of water is half full.
If you fill a cup of water completely, then empty half of the water, the cup is half empty.

If I told you I poisoned the water in the cup, would it matter if it's half full or half empty?

The cup is not half full or half empty. The cup may be 1/8 off of being half full/empty, but it would take mad skill to get the cup exactly half full/empty. I suggest you do not ask a question, but rather a statement, like, "The cup is 1/4 filled." or "The cup is 3/4 filled." I assume you noticed I said "Filled" instead of "Full" or "Empty". But, since there is the one in a million chance that one of us has some crazy awesome mad skill, I guess you should ask "Does the pot have half of the pasta it can hold?" but add "And you can't say if it's filled!". So, the cup is half filled.