This is a really interesting thing to think about. English is my mother tongue, and I'd never really considered this, it's always just been part of the language.

If I ask my partner to turn the volume "up," I am asking them to literally move the volume knob "upwards" towards the maximum limit. The physical motion doesn't literally track with televisions and remotes, for example, but you're still moving (turning) the volume upwards towards maximum.

That's how it shakes out in my head? You're moving something upwards towards the maximum. More is bigger, bigger is up.

“Fed up” as a phrase comes from feeding livestock up to their fill. It’s very similar to how you would say “filled up”. So the upness comes from raising the level up to the limit.

Let me clear that up for you!

First, regarding other languages, English gets this usage from its Germanic roots, and you still see that in languages like German, Dutch, Swedish, Danish, and Norwegian.

E.g. in German, words and phrases like "aufessen", "Iss deinen Teller auf", "austrinken", "Trink dein Glas aus". Dutch has "opeten" (eat up) and "opmaken" (use up). Swedish has "äta upp" (eat up) and "dricka upp" (drink up).

So really, English just inherited this and has had it for as long as English has existed.

In fact, the same seems to be true of Germanic languages - the widespread existence of this pattern suggests that it comes from proto-Germanic, the ancestor of Germanic languages spoken around 2000 years ago, or even from earlier Indo-European roots.

As for meaning, it's essentially a metaphorical use of "up" as meaning increasing, completing (fill up), appearing/emerging (come up), improving (touch up) - basically movement towards some completed or improved state which is metaphorically viewed as "up".

> Similarly with things like "fed up" (as in 'tired of'). Where is the "upness" here?

The upness is in having reached a maximum. An interesting comparison is "I've had it up to here!" which makes the metaphorical usage much more explicit.

It can also mean damage (blow up, tear up) or completeness (clean up, drink up).

> I don't think the semantics of "up" matters when I try to understand phrasal verbs like "turn up".

They don't, but they matter a lot when you're coining a new phrasal verb!

(They still matter a little for verbs that already exist. You might see a verb mutate from using one particle to using a different one, but that would probably take hundreds of years.)