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Consider the following example:

> divide the main folder into sub folders (in case of mail)
>
> フォルダを振り分ける  
>  フォルダをわける

What I want to know is why do we add "ふり"? Why can't we just use "フォルダをわけて"?
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2019-08-28T05:10:30.423
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2019-08-29T03:57:47.520
2020-06-17T08:18:27.500
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question
verbs compound-verbs
わける vs 振り分ける -- What is the ふり doing here?
According to goo辞書
[分ける](https://dictionary.goo.ne.jp/jn/195856/meaning/m0u/%E3%81%B5%E3%82%8A%E5%88%86%E3%81%91%E3%82%8B/)
/
[振り分ける](https://dictionary.goo.ne.jp/jn/195856/meaning/m0u/%E3%81%B5%E3%82%8A%E5%88%86%E3%81%91%E3%82%8B/):

**フォルダを分ける** to classify, to sort, to divide an aggregate into sub-folders
when you don't specify a purpose. Probably when a lot of miscellaneous things
in one folder, you might feel the necessity to divide the one folder into
several folders without specific labels for the moment.

**子供と大人に分ける** to split one group into the group of children and the group of
adults.

**大きさによって分ける** to classify by the size.

I think "分ける" is focusing on quantifiable things when you classify, split,
divide, etc.

**フォルダを振りわける** to classify, to sort, to divide an aggregate into sub-folders
when you have a specific purpose. Such as **生徒を理系と文系に振り分ける** to arrange
students into science majors and literature majors. They have some reasons for
the academic institutions to divide students into sub-categories.

I think **振り分ける** is focusing on the qualitative things when you classify,
split, divide, etc. such as **生徒を理系と文系に振り分ける** is implying classifying the
students with their aptitudes.

I do not know what 振り in 振り分ける is.

See also other sources: Weblio 類語辞典
[分ける](https://thesaurus.weblio.jp/content/%E5%88%86%E3%81%91%E3%82%8B) /
[振り分ける](https://thesaurus.weblio.jp/content/%E6%8C%AF%E3%82%8A%E5%88%86%E3%81%91%E3%82%8B)
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分ける just means dividing one thing (or several things) into two or more pieces
(or groups). 振り分ける means sorting or distributing _many_ things into subgroups,
and it is used especially when items arrive over time, as in e-mail filters or
HTTP load balancers. In your case, there is only one main folder but there are
many mails in it, so you can say メール **を** (サブ)フォルダ **に** 振り分ける or フォルダ **を**
2つのサブフォルダ **に** 分ける. フォルダ **を** 振り分ける doesn't look correct to me because it
sounds like there are dozens of random folders to sort.

Regarding this 振る, it means something like "to assign" here. See the third
definition [here](https://dictionary.goo.ne.jp/jn/195909/meaning/m0u/).
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answer