Opposition to “pretty”

Is his teacher a nativ English speaker (or at least British taught by the note of "mates" insted of friends)?

There's no good reason that I can think of aside from maybe he thought his students were saying it too much and he was trying to get them to note other words.

I see nothing wrong in the use of pretty as an adverb, although certain combinations could be amusing:-
"She's really pretty ugly."
"That's pretty bad."

I'm sure there are more.

:-))

Maybe because the meaning can be unclear - "very" or "somewhat" ?

Deeming "pretty" as informal seems to predate the wave of political correctness so I wonder wherher it was just some post-Victorian academic snobbery, in the same way as in the decade following WWII was taught at school not to use "get", which apparently was an ugly lower-class word. I would guess it was at school that I acquired (or got) the idea that "pretty" was unacceptable in formal writing. Blame the teacher(s)! Not sure where they got the idea from though.

With other words we have seen, just over one generation, "unseemly" become "inappropriate"; and words like "old", "elderly", "fat" become scarcely polite under the influence of political correctness, but the idea that "pretty" is informal seems to predate that.

@AnWulf - No, the teacher is Polish. I think the 'mates' bit was the words my student used.

@HairyScot - One of my English teachers used to give this example of the oddities of English:

' "Now, then", he said, giving me a pretty ugly look.'

'Pretty' was prety popular with British writers in the eighteenth and nineteenth centuries, especially with Daniel Defoe. Johnson gives eight examples, presumably approvingly. Even Lowth, and other grammarians used it in their books.

As to meaning, I like Johnson's definition best - 'it is less than very'. I can see why you might want to avoid it in academic texts (although both Darwin and Ruskin used it), but I would have thought that the same goes for 'very', so I don't really understand those who say use 'very' instead. For me, at least, they are not the same: 'petty' is more nuanced.

The only problem with "pretty" in this usage is that it is vague, like "kind of" or "sort of" (kinda, sorta). It's an empty intensifier, and appropriate only in informal speech. "Pretty much" isn't any better. "Somewhat" and "fairly" fall into this category, as well/

I accept that in certain academic work you might want something more specific, but for most of us, informal speech is what we use English for, the vast majority of the time. And that goes for my students as well, although of course we point out the differences between formal and informal buse.

But need it really be limited to informal conversation (or to fiction)? Some of the greatest 18th and 19th century writers of non-fiction would apparently disagree:

"I may mention that carnivorous animals, even from the tropics, breed in this country pretty freely under confinement," Charles Darwin - The Origin of Species

"His third tier, if not his second, will probably appear a sufficiently secure foundation for finer work; for if the earth yield at all, it will probably yield pretty equally under the great mass of masonry now knit together over it." John Ruskine - The Stones of Venice

"We may observe, that it is universally allowed by philosophers, and is besides pretty obvious of itself, that nothing is ever really present with the mind but its perceptions or impressions and ideas, and that external objects become known to us only by those perceptions they occasion."
David Hume - A Treatise of Human Nature

"The ice was melted for three or four rods from the shore, and there was a smooth and warm sheet of water, with a muddy bottom, such as the ducks love, within, and he thought it likely that some would be along pretty soon." Henry Thoreau - Walden

"Goethe's Tasso is very likely to be a pretty fair historical portrait, and that is true tragedy."
Ralph Waldo Emerson - Essays

I can't think of any word that would be more appropriate in these extracts, where something a bit less than 'very' seems to have been called for. Modifiers don't always have to be exact.

The Google ngram for "pretty good" is worth looking at. It seems to be on the increase curtrently