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


When did 役に立つ lexicalize to 役立{やくだ}つ?

Has 役立つ always been a word, and a word that is used more frequently than 役に立つ?
A quick google shows 役立つ is used 3 times more frequently.

I am reading the translation of a speech. The translator always says 役立つ where
I would say 役に立つ. Is there any connotation difference between the two? Maybe
役立つ less formal? My feeling is that initially there could be some association
of lexicalized words with "slang", but as time passes that perception goes
away.




Please refer to the other answer(s) for your main question (etymology).

As for the modern usage, the difference in frequency is not that large. Here
are the hit counts from BCCWJ.

  * 役に立 2302, 役に立つ 1039, 役に立っ 270, 役にたつ 94
  * 役立 3031, 役立つ 1419, 役立っ 447, 役だつ 30

役に立つ and 役立つ are not always interchangeable. As a simple predicate, 役に立つ is
the more common expression, and saying 役立つ sounds formal/literary/stiff.

>   * この辞書は役に立つ。 (perfect)
>   * この辞書は役立つ。 (sounds literary/stiff)
>

But 役立つ is preferred regardless of the formality, when another ～に precedes to
indicate the "type of usefulness". According to BCCWJ, roughly 80-90% of the
instances of 役立つ are preceded by such ～に.

>   * この辞書は勉強に役立つ。 (perfect)
>   * この辞書は勉強の役に立つ。 (also perfect)
>   * [?] この辞書は勉強に役に立つ。 (weird)
>

～に + 役に立つ is allowed in expressions like
「間接的に役に立つ」「私にとって役に立つ」「文法の勉強をするときにも役に立つ」, but the vast majority of the 役に立つ
examples are not preceded by に at all.

So 役立つ as a simple predicate is not as common as you might think.




Please refer to the other answer(s) for your main question (etymology).

As for the modern usage, the difference in frequency is not that large. Here
are the hit counts from BCCWJ.

  * 役に立 2302, 役に立つ 1039, 役に立っ 270, 役にたつ 94
  * 役立 3031, 役立つ 1419, 役立っ 447, 役だつ 30

役に立つ and 役立つ are not always interchangeable. As a simple predicate, 役に立つ is
the more common expression, and saying 役立つ sounds formal/literary/stiff.

>   * この辞書は役に立つ。 (perfect)
>   * この辞書は役立つ。 (sounds literary/stiff)
>

But 役立つ is preferred regardless of the formality, when another ～に precedes to
indicate the "type of usefulness". According to BCCWJ, roughly 80-90% of the
instances of 役立つ are preceded by such ～に.

>   * この辞書は勉強に役立つ。 (perfect)
>   * この辞書は勉強の役に立つ。 (also perfect)
>   * [?] この辞書は勉強に役に立つ。 (weird)
>

～に + 役に立つ is allowed in expressions like
「間接的に役に立つ」「私にとって役に立つ」「文法の勉強をするときにも役に立つ」, but the vast majority of the 役に立つ
examples are not preceded by に at all.

So 役立つ as a simple predicate is not as common as you might think.

