Emphasising circumstances: 是……的
特殊句型 / special sentence patterns
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
The 是……的 structure is used for an action that has already happened, when the focus is not the action itself (everyone knows it happened) but a circumstance: when, where, how, with whom, why.
Put 是 right before the focused element and 的 at the end of the sentence (or before a simple object: 我是昨天买的票). It works like English cleft sentences: "It was yesterday that I arrived."
In speech, 是 can be dropped in affirmative sentences (我昨天来的), but 的 cannot. The negative is 不是……的: 我不是坐飞机来的。
Examples
你是什么时候来北京的？
Nǐ shì shénme shíhou lái Běijīng de?When did you come to Beijing?
我是坐高铁来的，不是坐飞机来的。
Wǒ shì zuò gāotiě lái de, bú shì zuò fēijī lái de.I came by high-speed train, not by plane.
这个工作机会是朋友介绍的。
Zhège gōngzuò jīhuì shì péngyou jièshào de.It was a friend who told me about this job opening.
你是在哪儿学的中文？
Nǐ shì zài nǎr xué de Zhōngwén?Where did you learn Chinese?
Common mistakes
✗ 我是明天来的。 → 是……的 only describes past events. ✓ 我明天来。
✗ 我是昨天来了。 → no 了 in this pattern. ✓ 我是昨天来的。
✗ 我不昨天来的。 → negate 是 itself. ✓ 我不是昨天来的。