Noun を境にして

At a glance

Noun を境さかいにして means "with [noun] as the turning point" or "from [noun] on". It shows that a situation changed at a certain event or time, so the "before" and "after" are different.

Noun ＋ を境にして
Noun ＋ を境に

結婚けっこんを境さかいにして、彼かれの生活せいかつは大おおきく変かわった。 His life changed greatly after he got married.

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How to form it

The expression attaches directly to a noun. There are three common forms with the same meaning:

The noun is usually an event (結婚けっこん, 事故じこ, 卒業そつぎょう) or a point in time (四月しがつ, あの日ひ). The expression itself does not change. Politeness is shown at the end of the sentence.