B1
又…又… — both, and
How Chinese stacks two descriptions with 又…又 and 既…又, why the pair must agree in sentiment, and what to use instead when they do not.
Two qualities held at once, each with its own 又.
他又高又瘦。
Tā yòu gāo yòu shòu.
He’s tall and thin.
這兒的菜又便宜又好吃。
Zhèr de cài yòu piányi yòu hǎochī.
The food here is cheap and good.
No 很 anywhere — 又 is already holding the adjectives up, the way 比 and 越來越 do. That is a rule you will meet in every one of these patterns.
They have to point the same way
This is the constraint English does not have. 又…又 stacks qualities that agree in sentiment: both good, or both bad. It is a list of reasons, not a balanced assessment.
他又高又不聰明。
他很高，但是不太聰明。
One compliment and one complaint pull in opposite directions, and 又…又 has no way to hold both. A contrast wants 但是.
今天又冷又下雨，真討厭。
Jīntiān yòu lěng yòu xià yǔ, zhēn tǎoyàn.
It’s cold and raining today — miserable.
Both halves there are complaints, and the sentence is a pile of grievances rather than a description. That is what the pattern is for.
既…又 in writing
既 A 又 B is the more formal version and is common in written Chinese. 既 goes on the first and 又 on the second, never 既…既.
她既聰明又努力。
Tā jì cōngmíng yòu nǔlì.
She is both clever and hard-working.
既…也 also occurs and is interchangeable here.
Against 一邊…一邊
一邊…一邊 joins two actions happening together; 又…又 joins two descriptions that are true together. 他一邊走一邊打電話 is doing two things; 他又高又瘦 is being two things. Neither pattern accepts the other’s content.
And the other 又
又 on its own means again, of something that has already happened — 又/再/還. The doubled 又…又 is a different construction that happens to use the same character, and context separates them instantly.