才
cái
Expressing lateness with "cai"
才 after a time word says it happened later than expected — and never takes 了.
Subj. + Time + 才 + Verb
How it works
他二十五岁才上大学 — he didn't start university until twenty-five. The 才 conveys "not until".
It's the mirror of 就, which marks earliness. Compare 他八点就来了 with 他八点才来.
Crucially, 才 sentences don't take 了, whereas 就 sentences usually do.
Examples
tā èr shí wǔ suì cái shàng dà xué
他二十五岁才上大学。
He didn't start university until he was twenty-five.
tā shí èr diǎn cái shuì jiào
他十二点才睡觉。
He doesn't go to bed until midnight.
wǒ děng le yí gè xiǎo shí, tā cái lái
我等了一个小时，他才来。
I waited an hour before he turned up.
Common mistakes
- Don't add 了 to a 才 sentence.