Both 才 and 就 are adverbs that are used to express time or quantity. They are also used as conjunctions.
Time-related words + 就/才 + verb/adjective + (了)
“就” indicates that the speaker feels it is early or will happen in a short time; “才” indicates that the speaker feels it is late or it just happened not long ago. In this case, both are pronounced in a neutral tone.
e.g.
两点开会,他一点就来了。(Liǎng diǎn kāihuì, tā yīdiǎn jiù láile.) There was a meeting at two o’clock, and he came at one o’clock.
>> The speaker thinks he came early.
两点开会,他两点半才来。(Liǎng diǎn kāihuì, tā liǎng diǎn bàn cái lái.) There was a meeting at two o’clock, and he didn’t come until half-past two.
>> The speaker thinks he came late.
今天他八点就起床了。(Jīntiān tā bā diǎn jiù qǐchuáng le.) He got up at eight today.
>> The speaker thinks he got up early.
今天他八点才起床。(Jīntiān tā bā diǎn cái qǐchuáng.) He didn’t get up until eight today.
>> The speaker thinks he got up late.
“就” indicates that the speaker thinks having taken only a short amount of time; “才” indicates that the speaker thinks having taken a long time.
e.g.
这个会议开了40分钟就结束了。(Zhège huìyì kāile 40 fēnzhōng jiù jiéshùle.) The meeting ended after only 40 minutes.
>> The speaker thinks it took a short time.
这个会议开了40分钟才结束。(Zhège huìyì kāile 40 fēnzhōng cái jiéshù.) The meeting took 40 minutes to end.
>> The speaker thinks it took a long time.
我今天走了半个小时就到家了。(Wǒ jīntiān zǒule bàn gè xiǎoshí jiù dàojiā le.) I walked home for half an hour today.
>> The speaker thinks it took a short time.
我今天走了半个小时才到家。(Wǒ jīntiān zǒule bàn gè xiǎoshí cái dàojiā.) I walked for half an hour before I got home today.
>> The speaker thinks it took a long time.
“才” indicates that the speaker thinks the quantity is small, frequency or degree is low, while “就” indicates a large quantity, high frequency or degree.
e.g.
他很少迟到,可能一年才一次。(Tā hěn shǎo chídào, kěnéng yī nián cái yīcì.) He is rarely late, maybe only once a year.
>> The speaker thinks the frequency is low.
他经常迟到,这个星期就三次了。(Tā jīngcháng chídào, zhège xīngqí jiù sāncìle.) He is often late, three times already this week.
>> The speaker thinks the frequency is high.
“才” is often used with conjunction indicating reason or purpose, such as “只有……才……”, “因为……才……” or “为了……才……” and so on.
e.g.
为了你,我才开始学习汉语。(Wèile nǐ, wǒ cái kāishǐ xuéxí hànyǔ.) Because of you, I started to learn Chinese.
只有你开心,我才会开心。(Zhǐyǒu nǐ kāixīn, wǒ cái huì kāixīn.) I will be happy only if you are happy.
“就” is often used with hypothetical conjunction to indicate an assumption, such as “如果……就……” “只要……就……” “既然……就……” or “要是……就……” and so on.
e.g.
既然你想学习外语,就学习汉语吧。(Jìrán nǐ xiǎng xuéxí wàiyǔ, jiùxuéxí hànyǔ ba.) Since you want to learn a foreign language, learn Chinese.
要是你想学习汉语,就学吧!(Yàoshi nǐ xiǎng xuéxí hànyǔ, jiù xué ba!) If you want to learn Chinese, just learn it!
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