“Is the Glass Half Full, or Half Empty?”

This is a logical evaluation of the stated question. The answer is simple although it depends on the value of certain variables not stated in the question:

If the glass is in the process of being filled, then it would be half full.
If the glass is in the process of being emptied, then it would be half empty.

If the glass is holding a varying amount of liquid, that changes, prior to the glass being full or empty then:
If the glass is intended to hold liquid, then liquid is the intended unit of measure, and the glass is half full.
If the glass is intended to remain empty, then empty is the reference point for measure, and the glass is half empty.