1. At a specific time/age/stage
2. Emphasis on circumstances ("being ~, and yet…" / "precisely because of ~")
3. Combining two qualities ("both ~ and ~")
4. Set/idiomatic expressions
The grammar pattern にして has several distinct usages, all conveying the sense of "at (a particular point/condition)" or "under those circumstances." It is a literary and formal expression commonly found in written Japanese, speeches, and set phrases.
にして can mark a specific point in time, age, or stage at which something remarkable happens. It emphasizes that the event is noteworthy precisely at that point. This usage often carries a sense of surprise or admiration.
This is commonly seen with age expressions (〜~とし歳にして) or ordinal attempts (〜~どめ度目にして). A well-known classical phrase is おいて老いてなお, but the Confucian saying よんじゅう四十にしてまどわ惑わず ("At forty, one is free from doubt") is a famous example of this pattern.
Closely related to the first usage, にして can express the idea that something was only realized or achieved after reaching a certain stage. It often pairs with はじめて初めて to mean "only at (that point) for the first time."
にして can emphasize a particular status or condition, often with a nuance of "even for someone/something that is ~." This highlights that the result is unexpected given the stated condition.
にして appears in several fixed or semi-fixed expressions:
Do not confuse にして with にしては ("for ~, considering ~"), which is used for expressing that something is contrary to expectations based on a standard. Also note that にして differs from にしても ("even if"), though there is some overlap in the "even being ~" nuance.