It’s time to bury the glass half-full/half-empty metaphor. Here is the truth of it: If you are filling a glass, when you get to the halfway mark, the glass is half full. If you are emptying a glass, either by drinking it or pouring it out, when you get to the halfway mark, the glass is half empty. The amount of liquid in a drinking glass is an example of action not perception. And you know the truth of this. If I tell you a waitperson brought a bottle of wine and two glasses to the table and that a woman held out a hand when her glass was half full, you immediately presume the server had been filling the glass. If I tell you a waitperson brought two glasses of wine to the table and that a woman waited until her glass was half empty to begin to place her order, you immediately presume she’d been drinking the wine. In neither case does the partial glass of liquid leave you with a perception of optimism or pessimism. It’s merely a result of the action.
Even if it were a matter of perception, why is a “glass half-full kind of guy” considered to be a more upbeat, positive person than a “glass half-empty kind of guy”? Take for example a glass of very rare wine, so rare these are the last few ounces of its kind. While you are savoring every sip, delighting that half of a glass still remains, you can at the same time be experiencing the bittersweet knowledge that this glass of precious liquid is half empty. Which makes every remaining taste even more precious. In this case, the amount of liquid in the glass has nothing to do with positive or negative feelings and everything to do with appreciation.
If a glass with liquid in it is sitting on a table unattended, is it half full or half empty? I don’t care, and you shouldn’t either. You don’t know what it is, how long it has been there, who it belongs to, so it has no bearing on your state of mind. If this orphan glass is your responsibility to deal with or if you are a neat-freak who cannot bear to have unknown liquids lurking about, the glass is half empty because you will pour it out. Unless of course, you are so desperate for a drink you down the liquid despite its dubious origin. In which case, the glass is empty . . . and so is your stomach after you throw up.
So please, let’s bury this particular metaphor in the graveyard of moribund cliches and be done with it.