系（＝是）
is; was (formal written 是)
Structure
主语 ＋ 系 ＋ 名词性成分（身份、来源、原因） · …系…所致／所为
What it means
系 xì is a formal written 是: it links a subject to who or what it is, where it comes from, or what caused it.
How it is built
Subject + 系 + noun phrase; set frames 系…所致 (was caused by) and 系…所为 (was the work of): 这起火灾系电线老化所致 (the fire was caused by ageing wiring).
When to use it
News, police and court notices, official letters, museum labels. Short report verbs can follow (系伪造, 系误传). In speech it sounds like an official report: just say 是.
Watch out
No adjectives, no 系…的, no ✗不系: ✗这件事系很重要; negate with 并非 or 不是. Not 系 jì ‘to tie’ (系鞋带) or 系 ‘department’ (中文系).
Examples
2号墓的墓主系长沙国丞相利苍。
The occupant of Tomb 2 was Li Cang, chancellor of the kingdom of Changsha.
经鉴定，这批漆器系西汉初年的作品。
Experts have established that these lacquer pieces are works of the early Western Han.
据警方通报，这起火灾系电线老化所致。
According to the police statement, the fire was caused by ageing wiring.
Learn this in Lesson 175 · HSK 7–9: 马王堆 (The tombs of Mawangdui)
A dialogue, a reading, word cards with audio and a drill that uses it, in Learn Chinese with Bao. The first lessons of every level are free.
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