Emphasis with "jiushi"
As an adverb, 就 (jiù) can be placed before the predicate to add emphasis. It often has an intense or provocative feel to it, similar to "just," like how we sometimes say in English "it's just not right!" This emphasis very often appears as 就是.
Used as "Is Exactly"
就是 + Noun
- 那个 人 就 是 她 的 新 男朋友。That guy is her new boyfriend.
- 他 就 是 你 要 找 的 人 。He's just the person that you're looking for.
- 我们 就 是 他 的 家人 。We're his family.
- 你 就 是 个 笨蛋！A moron is precisely what you are!
- 他 就 是 那 个 骗子！That conman is him!
Used as "only Because"
就是 can be used to intensify the predicate to mean "only (because of) that and nothing else." In this case, 是 can't be omitted. In many cases, you could also add in an 因为, but it's not required.
- 他 不 去 旅游 就是 不 想 花钱 。 He didn't travel only because he doesn't want to spend the money.
- 你 不 参加 比赛 就是 怕 输 吗 ？ You're not entering the competition just because you're afraid of failure?
- 他 这样 说 就是 嫉妒 我 。 He said this only because he envies me.
- 她 问 这么 多，就是 担心 你 。 She asked so many questions only because she's worried about you.
- 她 就是 漂亮 ，没 别的 优势 。 She's just pretty; she doesn't have any other strengths.
In the examples above, 就 pairs exclusively with the verb 是. But 就 can also come before other verbs, with similar emphatic effect. In these cases, it's also OK to use 就是 before the other verbs as well.
就(是) + (不) + Verb
- 我 就 要 去！I just want to go!
- 我 就是 喜欢 他。I just like him.
- 我 就 不 告诉 你 。I'm just not going to tell you.
- 我 父母 就是 不 让 我 一个人 去 。 My parents simply won't let me go alone.
- 这个 学生 就是不 听 老师 的 话 。The student just wouldn't listen to his teacher.
As you may have noticed, many of these uses of 就 or 就是 carry a flippant, stubborn tone, referred to as 任性 (rènxìng) in Chinese.
- "Just" with "jiu"
- Comparing "cai" and "jiu"
- Events in quick succession with "yi... jiu"
- Expressing earliness with "jiu"
- Expressing indifference with "jiu"
- Limiting scope with "jiu"
- "If…, then…" with "ruguo…, jiu…"