Subject + 是 + [Time/Place/Manner/Agent] + Verb + 的
是...的 (shì...de) — emphasizing the time, place, or manner of a past event
When both speaker and listener already know THAT something happened, 是...的 zooms in to emphasize the circumstances — when, where, how, or by whom it happened — rather than the bare fact that it happened (that's what plain 了 is for): 我是昨天到的 (it was YESTERDAY that I arrived — emphasizing when), 他是坐飞机来的 (it was BY PLANE that he came — emphasizing how). 是 can often be dropped in casual speech (especially in statements, less so with negation), but 的 at the end is required. Because the event is already known to have happened, 了 does NOT appear inside this pattern — 我是昨天到了的 is wrong; 是...的 replaces the need for 了 entirely. The deciding question: is the fact that it happened already established/obvious, and do I want to spotlight WHEN/WHERE/HOW/WHO specifically (→是...的)? If the fact itself is new information, use plain 了 instead.
Examples
- 我是昨天到的，不是今天。wǒ shì zuó tiān dào de, bú shì jīn tiān
It was yesterday that I arrived, not today.
- 他是坐飞机来的。tā shì zuò fēi jī lái de
He came by plane.
- 这本书是我在北京买的，是去年买的。zhè běn shū shì wǒ zài běi jīng mǎi de, shì qù nián mǎi de
I bought this book in Beijing — I bought it last year.
Common mistake
✗ Wrong: 我是昨天到了的。
✓ Right: 我是昨天到的。
了 doesn't appear inside 是...的 — the pattern already marks the event as a known, completed fact, so 的 alone closes the sentence, without an extra 了.
Practice this pattern
Fill in the missing character:
我＿昨天到的，不是今天。
It was yesterday that I arrived, not today.