Both… and…: 既……又 / 也
复句 / complex sentences
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
Subject + 既 + A，又 / 也 + B
既……又…… (jì… yòu…) = "both A and B". The two qualities or actions coexist. It's a bit more formal than 又……又…….
A and B are usually of the same type (two adjectives, two verbs) and point in the same direction (two good points, or two bad ones).
Variant: 既……也……, slightly more written.
Examples
我的新同屋既热情又大方。
Wǒ de xīn tóngwū jì rèqíng yòu dàfang.My new roommate is both warm and generous.
好朋友既能一起玩儿，也能一起吃苦。
Hǎo péngyou jì néng yìqǐ wánr, yě néng yìqǐ chīkǔ.Good friends can both have fun together and go through hard times together.
她既是我的同事，又是我最好的朋友。
Tā jì shì wǒ de tóngshì, yòu shì wǒ zuì hǎo de péngyou.She's both my colleague and my best friend.
Common mistakes
✗ 他既聪明，又懒。 → awkward: both items normally point the same way. For a contrast: 他很聪明，却很懒。
✗ 既……还…… → ✓ 既……又…… / 既……也……