Who decided "up" and "down" were the proper terms for up and down?

Good question, Val - I'm glad you asked. It is my opinion that some words just sound correct. This is no accident. Since the advent of spoken language, there has most likely operated a secret committee that convenes every five or six years to determine the proper phraseology for an action or item. There is probably a secondary group in charge of adverbs, pronouns and conjunctions, but this is in all likelihood more of a maintenance functionality than a festive coining of new, colorful, deftly-appropriate naming conventions. I have not yet been able to prove the existence of such a group (or groups), but you can be sure that I am diligently working the dark, seedy underbelly of the language community to provide ironclad proof of such a society.

The words "up" and "down" were used to their most exciting capacity in the days of the Roman gladiators. Ironically, the words were not even spoken, but were signalled by the iconic pointing of the thumb in an upward or downward direction to signal the survival or execution of a vanquished gladiator. Good thing, too, because the words would have been "su" or "gui", which were obviously not run by the committee before being put into circulation.

For the most part, the committee in charge of the English words have done a phenomenal job of crafting the appropriate terms for the actions or items to which they are assigned. "Shit" is one of my favorites, having just the proper brevity, soft consonants and hard ending to convey the noun or the verb or the vulgar exclamation. As close to a perfect word as will be found rolling off the English-speaking tongue in its variety of contexts. So popular is this word, in fact, that it is usually one of the first words those for whom English is not the mother tongue learn to utter, with all their cute little accents.

Now for the science.

Apparently, the word "up" was derived from the Teutonic "uf", meaning "over. I believe the committee did a fine job softening up the word from the often harsh Teutonic pronunciation, which can frankly be off-putting, giving the word a little pop and allowing for a more pleasant feel to its utterance. As it should be.

The word "down" comes from the Old English word "dune" or "hill": and this makes some sense I suppose, since it was probably coined when Jack fell "down" and broke his crown while fetching a pail of water. He was rolling down a hill. It all makes sense in an old English kind of way.

I hope to one day gain a seat on the Word Committee and eventually chair its ranks. Until then, it's "thumbs up" for a question well-asked. Huzzah!

And good day, Sir.