I awoke and stared at a children's book on my floor. It was upside down. Where did we get the phrase upside down? It is literally the up side being down. I looked up the etymology of the word and I was wrong. Here's the real way the word came about:
Upside down comes from Middle English upsadoun, or the combination of up so down. So meant as if, so it meant up as if down. Nothing to do with the word side. Upside down first appeared with side in the late 1500s. Earlier written versions retained so.
How did side come into our phrase upside down?
Somewhere along the line, we probably confused the 'sad' of upsadoun to mean side. Without widespread literacy or writing, humans rely on sound to make meaning. We have the word upside which is up + side that came into Enlish several hundred years later (1610 written). The phrase inside out is literally in+side+out historically. I wondered if side was related to the word so, but side is from a separate root Old English sid (which means long). Considering these phrases, upside down seems like it should have been side and not so originally.
The side in upside down makes more sense in my mind than up so down. Middle English speakers thought so too. Maybe I should just write and say up so down and see if anyone understands me. How many blank looks do you think I'll get?