How did a rough breathing develop before all words starting with an upsilon in Ancient Greek? This is a commonly noted fact about the distribution of these sounds (or rather spellings), but I’m having a hard time figuring out the etymological reason for it.
In some words, it is easily explicable as the regular outcome of a word-initial *s- in Proto-Indo-European: *súpnos > ὕπνος (húpnos)
But in other words, there is no *s reconstructed for the PIE form. Are there any historical linguistics hypotheses about the source of the rough breathing in these words (e.g. a prothetic *s- prefix that later weakened to a rough breathing, a shift [w] > [v] > [f] > [h], a sound change inserting /h/ before all word-inital /u/ at some point in Ancient Greek (that seems phonetically unmotivated to me, although I guess it's the most straightforward option), something like that).
Some example words (I’m taking these from Wiktionary):
- *wódr̥ > ὕδωρ (húdōr)
- *webʰ- > ὑφαίνω (huphaínō)
- *upo > ὑπό (hupó),
- *uperi > ὑπέρ (hypér)
Are these last two related to the prothetic s- seen in Latin sub, super? (Wiktionary gives super < *eks-uper, but ὑπέρ < *uperi, which would seem to suggest that it is just a coincidence).
A related question: a rough breathing seems to also have developed in some words that didn't start with upsilon, but that had *w in their PIE form. In most words starting with *w in PIE, like *wérǵom > ἔργον (érgon) the *w simply developed to ϝ (representing the sound /w/) and was later lost, leaving a smooth breathing behind. Why did a rough breathing develop in the following words?
- *wek(ʷ)speros > ἕσπερος (hésperos)
- *wes- > ἕννυμι (hénnumi)
Is this related to the *s that comes later in each of these roots?
I don't know if it's also relevant that the PIE word-initial cluster *wr- merged with the reflex of the cluster *sr- in Greek, giving ῥ (rh, rho with a rough breathing).