100224
My guess is that the phrase is derived from the composition of the following:

  1. 役 (yaku) : service, use

  2. に：particle for destination

  3. 立った：perfective of 立つ (tatsu)

So it's extended meaning like "rise to a supporting role", "being supported".

Am I more or less correct?

===

I have read posts:

[Is "役立つ" a recent lexicalization of "役に立つ"? Is it less
formal?](https://japanese.stackexchange.com/questions/36268)

[Difference Between 手伝う, 力になる, and
役に立つ](https://japanese.stackexchange.com/questions/87629)
CC BY-SA 4.0
2023-07-08T11:59:49.617
100211
2023-07-08T22:46:39.953
56969
question
grammar words syntax expressions particle-に
How is 役に立った ( helpful ) formed?
Your reasoning is correct. But I think that in this context the meaning of 立つ
is "to stand still" rather than "to rise".

に doesn't function as a particle of destination but as an adverbializer (look
the last entry [here](https://en.wiktionary.org/wiki/%E3%81%AB). It modifies
the verb, it tells us how the verb is performed.

So in a sentence like:

> それは役に立つ。

それ is the subject who stands up (立つ) in a way that is helpful (役に).

You may have other aditional に particles indicating time, location, etc.

Have in mind that the subject is not always what marked by は. For example:

> 俺にしてはとても役に立つ。

Meaning: As for me, (it) is really helpful.

The subject is always marked by が, but when it is not present you'll have to
deduce it from context.
CC BY-SA 4.0
2023-07-08T13:02:11.817
100212
2023-07-08T13:02:11.817
56959
100211
answer
役に立つ is a fixed phrase that has to be learned by rote, but if I really have to
analyze it...

  * **役** : "service", "use"
  * **に** : Here, it's a role marker rather than a destination marker. In other words, it's more like "as X" or "for X" rather than "to X". See: [Can に have the same function as として?](https://japanese.stackexchange.com/q/82913/5010)
  * **立つ** : This is a [light verb](https://ell.stackexchange.com/a/42912/8629) that has [dozens of possible translations](https://jisho.org/word/%E7%AB%8B%E3%81%A4) including "to form", "to work/serve (as)", "to excel (at)", "to be viable", "to be realized", "to be made" and so on.

So a super-literal translation of 役に立った would be "served for (some) use" or
"was viable as service".

Similar set phrases where 立つ is used in a similar manner include:

  * 予定が立つ
  * 腕が立つ
  * 申し訳が立つ
  * 面目が立つ
CC BY-SA 4.0
2023-07-08T22:46:39.953
100224
2023-07-08T22:46:39.953
5010
100211
answer