[zarzavat]

‘O’ has an interesting backstory. The shape comes from phonecian ayin and has the meaning of “eye”, from which it takes its form. It probably had a sound close to the Arabic ayin (a kind of guttural growl where you half choke yourself).

However the Greeks were probably just as confused by that sound as non-Arabs are by it today, so they instead gave it a vowel sound.

‘A’ had a similar story. In Phonecian it represents a glottal stop and has the name ‘alep. However a glottal stop at the start of a word is quite hard to hear if you aren’t used to it, so the Greeks seemingly assumed that the letter represented the second phoneme of ‘alep, an /a/ sound. Hence the alphabet was invented, a mixture of vowels and consonants with equal status.

[tragomaskhalos]

It's really a lucky happenstance that Semitic languages have enough gutterals that could be repurposed as vowels; if these had been lacking, or if Greek had needed them as consonants, then it's easy to imagine a sort of incomplete consonant-only orthography coming into use, perhaps even persisting to Latin alphabets in the modern day. Greece's first introduction to writing (linear b) didn't stick and doesn't seem to have been used for anything other than palace records, arguably because of deficiencies in that script, might literacy in the West have similarly been stunted by scripts that could not show vowels?

[HPsquared]

We could get by without most vowels anyway, that's basically SMS text speak.

We cld gt by wtht mst vwls aynw, tht's bscly SMS txt spk.

[gumby]

Losing the vowels works in languages like Arabic because of the structure of the language, with consonantal clusters (e.g. ktb, tlb) being semantic “roots”. So you usually know from context, and if you don’t know the absolutely precise word, you know the meaning, which can sometimes be more informative.

Indo-European languages don’t work that way.

[zarzavat]

It’s not a hypothetical actually. Many non-Semitic languages have adopted Semitic writing systems. e.g. Persian, Urdu, Yiddish.

Sometimes they always write the short vowels in, e.g. Urdu and Yiddish, but other times they don’t e.g. Persian.

So it’s at least possible to write an Indo European language without vowels. Desirable? Probably not.