How is 役に立った ( helpful ) formed?

Question

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?

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I have read posts:

Is "役立つ" a recent lexicalization of "役に立つ"? Is it less formal?

Difference Between 手伝う, 力になる, and 役に立つ

Answer 1

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?
• 立つ: This is a light verb that has dozens of possible translations 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

Answer 2

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. 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.