JLPT N1Mostly written

を境さかいにfrom … on, things changed

Things were one way up to a certain point and have been different ever since. を境さかいに names that point.

引ひっ越こしを境さかいに、車くるま中ちゅう心しんの生せい活かつから公こう共きょう交こう通つうを使つかう生せい活かつへ変かわった。

Moving marked a change from a car-centered lifestyle to one based on public transportation.

How to form it

Noun + を境に（して）

The して is optional and changes nothing.

Before it: A date, an age or an event: 2019にせんじゅうきゅう年ねん, 三さん十じゅっ歳さい, 結けっ婚こん, 退たい職しょく, その日ひ.
After it: How things have been since: 〜ようになった, 〜なくなった, 急きゅう増ぞうした, 減げん少しょうに転てんじた.
Said about: Anything: your own life, someone else's, a line on a graph. The change can be for better or for worse.
Where you'll meet it: News, reports, biographies, documentary narration, novels. In conversation people mostly say 〜てから.

In use

それまで横よこばいだった空あき家や数すうは、2019にせんじゅうきゅう年ねんを境さかいに急きゅう増ぞうした。

The number of vacant homes, which had previously been stable, rose sharply from 2019 onward.

退たい職しょく前まえは仕し事ごと中ちゅう心しんだった父ちちは、退たい職しょくを境さかいに地ち域いき活かつ動どうへ積せっ極きょく的てきに参さん加かするようになった。

Before retiring, my father centered his life on work; after retirement, he began actively participating in community activities.

その日ひを境さかいに、彼かれは学がっ校こうに来こなくなった。

From that day on, he stopped coming to school.

その日ひを境さかいに, "from that day on", is a favorite of novels and documentaries.

Two things to know

What follows has to last

After を境さかいに comes the way things have been ever since. Something that simply happened once afterward doesn't fit.

Not said: 退たい職しょくを境さかいに、父ちちはハワイへ旅りょ行こうに行いった。

(After retiring, my father went on a trip to Hawaii.)

For one thing that happened afterward: 退たい職しょくしてから or 退たい職しょく後ご.

In conversation it's てから

結けっ婚こんを境さかいに、兄あにはたばこを吸すわなくなった。

From the day he got married, my older brother stopped smoking.

Written. It draws a line at the wedding, with a different life on each side.

結けっ婚こんしてから、兄あにはたばこを吸すわなくなった。

My older brother stopped smoking after he got married.

What you'd say to a friend.

Close neighbours

を機にN1

Someone takes the event as the occasion to start something new, usually by choice. を境さかいに only reports that things changed.

海かい外がい赴ふ任にんを機きに、現げん地ちの歴れき史しを学まなび始はじめた。

I took my overseas assignment as an opportunity to begin studying local history.

を限りにN1

The date is the last time. Something ends there.

彼かれは今年ことしを限かぎりに引いん退たいする。

He will retire at the end of this year.

て以来N2

Something has gone on without a break from then until now. No contrast with before is needed.

日本にほんに来きて以い来らい、一いち度ども国くにに帰かえっていない。

I haven't been back to my country once since I came to Japan.

Check yourself

1Which sentence sounds natural?

Choose an answer to see why.

2Which one fits?

結けっ婚こん（　　）、二人ふたりは家いえを買かった。

Choose an answer to see why.

More detail

境さかい is a border, and the same words work for a real one.

この川かわを境さかいに、町まちは東とう西ざいに分わかれている。

The town is divided into east and west, with this river as the boundary.

More sentences

それまで増ふえ続つづけていた申しん請せい件けん数すうは、新しん制せい度どの導どう入にゅうを境さかいに減げん少しょうに転てんじた。

Applications had continued to rise, but began declining after the introduction of the new system.

大だい規き模ぼな災さい害がいを境さかいに、地ち域いきの防ぼう災さい意い識しきは大おおきく変へん化かした。

The major disaster marked a substantial change in the community's approach to disaster preparedness.

三さん十じゅっ歳さいを境さかいに、健けん康こう管かん理りを以い前ぜんより意い識しきするようになった。

Turning thirty marked the point when I became more conscious of managing my health.

春はるの大たい会かいを境さかいに、彼かの女じょの成せい績せきは安あん定ていして上じょう位いを保たもつようになった。

After the spring tournament marked a turning point, her results stabilized and she began consistently placing near the top.