It’s definitely about vowel sounds, because we don’t say “a hour” or “a herb”.

> It’s definitely about vowel sounds

Exactly, and Nvidia begins with an e sound.

And we say "a union" because it begins with a y sound and not because it begins with the letter u.

In the UK, people do say "a herb", but that's because we pronounce the h: https://en.wiktionary.org/wiki/herb#Pronunciation

> a herb

I do, but that's because I pronounce the 'h' in 'herb'.

"we" being Americans: the rest of the English-speaking world says "a herb" as the "h" in "herb" is not silent

An historic day!

That's just weird over-correction. "A historic day" is correct but for some reason people heard "An historic day" and the idea spread that it was a special exception.

Kind of like how you see lots of people on Reddit saying "water isn't wet, it just makes other things wet". They heard someone else say it and it sounds smart so they repeat it, without spending 10 seconds to look it up in a dictionary.

To me it may be a tell for the writers at one point pronouncing it as "'istoric", similar to those who say human as "'uman", and then as you said likely fanning out as an over-correction, possibly because that dialect was associated with prestige.

Yes maybe once upon a time but it doesn't explain why people say "an historic" today.

I an struggling to understand what is wrong with the phrase "water isn't wet, it just makes other things wet". Can you explain?

Water is wet. There's nothing wrong with it grammatically. I just meant it was an example of people blindly copying untrue but smart-sounding facts.

deleted; i misread the parent comment

"hour" starts with an 'o'-sound, since the 'h' is (mostly) silent, so "an hour" is correct.

Be careful though. There are words that start with a vowel when written, but are pronounced with a consonant. Eg "a universe".

HN battling over grammar which is a standard. Focus on topic!

Yeah the rule is just "which one sounds better?". That's why "an" exists in the first place - because saying "a nvidia" is super awkward.