How to Tell the Difference

Not in a vacuum.

Meh.

If in a vacuum, it's filled with dark matter.

I always say that the glass is too big...

Yeah but aren't atoms like 99.999999999% empty space? When considering the whole volume of the glass, the percentage of space taken up by mass-possessing particles is absurdly low. The glass is always empty.

And don't forget the engineer take, which has been featured on Neatorama on Feb 9, 2008: "An optimist will tell you the glass is half-full; the pessimist, half-empty; and the engineer will tell you the glass is twice the size it needs to be".

Convert the water to ice and replace the air with 12 year old Scotch, and the glass is perfect.

@Yep: really, ICE with Scotch? oops

It is assumed that the question is "Is the glass half-full or half-empty OF WATER." Too bad "geeks" fail at pragmatics. Us normal people get it just fine.

Replace the water with beer, and the glass is halfway towards ordering another.

@No (#9): Assumption is the mother of all screw-ups. Geeks, as a rule, try to avoid assumptions.

Geeks are always full of it.

why do all the people below me have to be such smartasses..

That glass is twice as large as it has to be.

@No (9)

I agree with Falko. You are ASSUMING the glass is halfway filled with WATER. You could just as easily assume the glass is half full of apple juice or dirt. I've never heard the saying specify WHAT the glass is half full or empty OF.

lol. :)

I love it. In fact, I thought of this years ago and have just continued to wait until someone asked it the glass was half full or half empty, so I could give my neither-optimistic-nor-pessimistic version, but one that transcends both!

Of course, being a scientist myself, I have always been worried with the flaw in an otherwise beautiful and unexpected answer. For a while I almost changed my stock answer to "It's less than 1 percent full, actually about a billion times less. But I love the "all full" answer so much better.

I did appreciate Gupta's "twice the size it needs to be" comment...

Nevertheless, the glass *is* half full of water the second most important substance of our lives. How is it that so many people forget the glass is also half full of air - *the* most important substance in our lives!!!!

@No

Apparently normal people fail at having a sense of humor.

Also, normal people don't use the word "pragmatics".

The realist sees a dirty glass and knows it will need washing.

Actually there exists no glass.... Its all multiple dimensions!

Logic tells me...
When the glass was created, it was empty.
Therefore, the glass is now half full.