Yep "correctness" only exists contextually. A language teacher can say "no that's wrong" with the implied meaning of "that doesnt follow the patterns of the dialect I'm teaching you". Ditto for newspaper editors and their house style.
But in 99% of situations no such context exists and "that's grammatically incorrect" is a bullshit statement.
In the UK when someone "corrects" language what they are very often doing is engaging in class signalling. It's widely done and widely accepted but personally I think it's pointless and somewhat toxic.
(Note many languages have government-sanctioned standard forms of the language, but what I said is still true there too. Nobody speaks that dialect and nobody should be expected to. It's just a "reference implementation".)
I don't think all correction is merely class signaling. Sometimes it's teaching others how to properly class signal, which is slightly less cynical. We all judge others based on the grammatical or spelling errors that others make. At least being aware of them gives you a chance to choose which ones you care about.
>But in 99% of situations no such context exists
Only the ones where your manner of speaking doesn't influence how the recipient thinks of you.
Good luck.
> In the UK when someone "corrects" language what they are very often doing is engaging in class signalling.
Same is true in the US, though ethnicity is in the mix too. White and black Americans are historically distinct cultural groups which speak different dialects (though obviously, since the end of slavery and segregation the groups are mixing more and more). It is no coincidence that varieties spoken by white people ended up as the “standard”.
> Note many languages have government-sanctioned standard forms of the language, but what I said is still true there too. Nobody speaks that dialect and nobody should be expected to. It's just a "reference implementation".
Many of those languages have mutually unintelligible dialects. The reference implementation exists to patch communication when you run into trouble with people who aren’t from your village.
Even American English has this. People from Appalachia register switch to more standard English when they’re not home, for example. Or a high schooler will tamper their slang when talking to grandma.
You could also argue international business English is a contrived dialect used primarily by ESL speakers. It definitely has many differences from any English spoken natively at home.