是 ... 的 — focusing the time, place, or manner of a past event
是 ... 的 is a frame that wraps around a PAST event whose existence is already known and asks (or answers) about a specific detail — WHEN, WHERE, HOW, or WITH WHOM it happened. Shape: (subject) + 是 + [time / place / manner / agent] + verb + 的. 我是昨天来的。 = I came yesterday (it was YESTERDAY that I came). 他是从北京来的。 = He came from Beijing. 她是开车去的。 = She drove there (went BY DRIVING). The key contrast is with bare 了: 我昨天来了 simply reports the event ('I came yesterday'); 我是昨天来的 asserts that the time was yesterday — answering or implying the question 'when?'. Don't use 是 ... 的 for events that haven't happened, future plans, ongoing states, or for the very first time you mention an event.
The shape — and what slots between 是 and the verb
Between 是 and the verb, you put the focused element. Common fillers: TIME (昨天, 去年, 三点), PLACE / SOURCE (从北京, 在学校), MANNER (开车, 坐火车, 一个人 = alone), AGENT (我朋友). Then comes the verb, and 的 at the end. 我是昨天来的。 (when). 他是从北京来的。 (place / source). 她是开车去的。 (manner). 这本书是他写的。 (agent — 'this book was written by him'). Note: 是 is often DROPPED in affirmative sentences when the speaker is relaxed: 我昨天来的 can stand on its own. 的 is non-negotiable. In negation, 是 becomes mandatory: 我不是昨天来的。 = It wasn't yesterday that I came.
是...的 vs. bare 了 — different jobs
我昨天来了。 = I came yesterday. (Plain past report — both that I came AND when are new info.) 我是昨天来的。 = It was yesterday that I came. (My coming is already established; the new info is WHEN.) Use 是 ... 的 when (a) the listener already knows the event happened and (b) you're zooming in on a specific detail. A textbook diagnostic: if the question was 'When/Where/How did you come?', the answer takes 是 ... 的. If the question was 'Did you come?', the answer takes 了. Don't stack both: 我是昨天来了的 is wrong. Pick one frame.
Word order — and where the object goes
When the verb has an object, you have two choices. Object BEFORE 的 (most common, especially in speech): 我是在北京学的中文。 = It was in Beijing that I studied Chinese. Object AFTER 的 (also fine): 我是在北京学中文的。 Both work; the first is slightly more colloquial. With pronouns, the object usually goes after 的: 他是昨天告诉我的。 = It was yesterday that he told me. With NO object, the 的 simply ends the sentence: 她是开车去的。 Don't insert 的 in the middle just because there's a verb-object compound — keep the compound together when natural.
Negation, questions, and short answers
Negation uses 不是 ... 的: 我不是昨天来的,我是今天早上来的。 = I didn't come yesterday — I came this morning. (You're correcting the FOCUSED element, not denying the event.) Questions use 是 ... 的吗 or a wh-word in the focus slot: 你是什么时候来的? = When did you come? 你是怎么来的? = How did you come? 你是从哪里来的? = Where are you from? (= 'where did you come from'). These three are everyday, must-know questions. Short answers can keep 是 + the focus + 的: 'Q: 你是怎么来的? A: 我是开车来的。' = 'How did you come? I drove.'
When NOT to use 是...的
(1) Future events — 是 ... 的 is for COMPLETED events. 明天我去 is fine; 明天我是去的 is wrong. (2) Ongoing or habitual states — 我每天六点起床 (I get up at 6 every day, habit) takes no 是 ... 的. (3) The very first mention of a brand-new event — if your listener doesn't yet know that you came, lead with 我昨天来了, then if they ask follow-up details, switch into the 是 ... 的 frame. (4) 是 ... 的 about ORIGIN can sometimes feel adjectival rather than past-event, e.g. 他是中国人 (he's Chinese) — that's a bare 是 + noun structure, not the past-focus 是 ... 的. Don't confuse the two frames.
