Past experience: 曾经
副词 / adverbs
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
曾经 (céngjīng) means "once, at some point in the past, have (ever) done". It shows that an action or state existed in the past and is over now. It very often goes with 过 or 了.
It sounds a bit more formal than plain 过, which makes it perfect for talking about your background: in a job interview, for example.
Don't confuse it with 已经 (already): 已经 says something is done as of now and its result still matters; 曾经 points to a finished past.
Examples
我曾经在一家外国公司工作过两年。
Wǒ céngjīng zài yì jiā wàiguó gōngsī gōngzuò guo liǎng nián.I once worked for a foreign company for two years.
他曾经是我们学校的老师。
Tā céngjīng shì wǒmen xuéxiào de lǎoshī.He used to be a teacher at our school.
我曾经想当医生，后来改变了主意。
Wǒ céngjīng xiǎng dāng yīshēng, hòulái gǎibiàn le zhǔyi.I once wanted to be a doctor, but later I changed my mind.
这里曾经有一个很大的公园。
Zhèlǐ céngjīng yǒu yí ge hěn dà de gōngyuán.There used to be a big park here.
Common mistakes
✗ 我曾经吃饭了，不饿。 → the result matters now, so use 已经. ✓ 我已经吃饭了，不饿。
✗ 我没曾经去过。 → in the negative just use 没(有)……过. ✓ 我没去过。