"Rather" is an adverb used to modify the adjective "beautiful". It can mean either "slightly" or it can mean "highly". In this context, it is a gentle (as opposed to extreme) affirmation and emphasizes the adjective. It does not indicate surprise nor is it degrading. It is like saying, "You are quite beautiful" (another acceptable translation) or even "You are very beautiful". Another example: "I did rather well on the exam." It means that I performed well and am very pleased with the outcome. http://dictionary.cambridge.org/us/dictionary/british/rather
I'll try. Not so much "assez" but "plutôt", in the same sense of "Elle est plutôt jolie" = She is quite pretty. It amplifies or reinforces the adjective somewhat without exaggerating it. I.e., "quite pretty" to me means that, "she truly is attractive." It is an affirmation that the adjective being used is genuine. So, what is the difference between "beautiful" and "quite beautiful"? Not much more than the assurance that the adjective is being applied toward the top of the scale, IMO. On the opposite side, one could say that "She is rather plain" as the polite version of "She does not possess any particularly attractive features." "She is quite plain" is similar, but moreso, with "quite" emphasizing "plain". So in that sense, "quite" is a bit closer to "très". "Quite" is a little stronger than "rather" in this regard although both might be used for plutôt. So in order of intensifying from least to most: 1) rather, 2) quite, 3) very. I hope this is helpful.
This is helpful, thanks.
I have understood that "quite" can understate the following adjective to an extent that depends on the very meaning of the adjective.
A few more details, please: when does "quite" mean "absolutely"?
Should I understand "not quite" as "pas tout à fait" or as "pas du tout"?
Should I understand "you are quite right" as "tu as tout à fait raison" or "tu n'as pas tout à fait raison"?
"you are quite right" means that you are completely, unequivocally right.
"the film was quite good", "she's quite a good actress", "he's quite handsome" - complimentary, but would be more complimentary without the "quite". BUT, e.g. "quite brilliant", "quite perfect" are more complimentary with the "quite".
plutôt is being used as an intensifier here so rather/quite are used in English to emphasize the beauty or in the sense of "rather expensive" (il est plutôt/assez cher). "You are instead beautiful" does not make any sense. The sentence "I'd rather (have) a blue one" indicates a preference, so perhaps Je préfère un bleu. would work better. http://www.larousse.com/en/dictionaries/french-english/plut%C3%B4t/61128