Why the specific spelling "一つひとつ"?


I'm reading a book and the author keeps using the spelling "一つひとつ" for "one-
by-one". I found this a bit curious: The word itself is just a doubled 一つ, so
why not spell both parts the same? Does writing it that way convey a certain
nuance which 一つ一つ or 1つ1つ do not?




This is a matter of personal taste. If the author did this intentionally, I
believe they were trying to emphasize the nuance of ひとつひとつ by covering various
possible spellings. Similar examples include
[長いながい道](https://www.amazon.co.jp/dp/4036340107/) and
[すき、好き、大スキ](https://www.amazon.co.jp/dp/4883816192/). One may also argue that
switching kanji/kana too much in a single word is visually displeasing, but I
personally doubt that is the main reason.

Here are the hit counts of BCCWJ:

  * ひとつひとつ: 604
  * 一つ一つ: 1005
  * 一つひとつ: 293
  * ひとつ一つ: 5

* * *

**EDIT:** This is not limited to 一つひとつ...

  * おそるおそる: 224; 恐る恐る: 193; 恐るおそる: 9; おそる恐る: 0
  * おもいおもい: 2; 思い思い: 183; 思いおもい: 9; おもい思い: 0
  * かさねがさね: 8; 重ね重ね: 24; 重ねがさね: 3; かさね重ね: 0
  * たびたび: 823; 度々: 354; 度たび: 4; たび度: 0

Maybe the users of 度たび／恐るおそる are treating the second part somewhat like a long
okurigana...? I personally do not do this, but it is true that there are
writers who like this style.




This is a matter of personal taste. If the author did this intentionally, I
believe they were trying to emphasize the nuance of ひとつひとつ by covering various
possible spellings. Similar examples include
[長いながい道](https://www.amazon.co.jp/dp/4036340107/) and
[すき、好き、大スキ](https://www.amazon.co.jp/dp/4883816192/). One may also argue that
switching kanji/kana too much in a single word is visually displeasing, but I
personally doubt that is the main reason.

Here are the hit counts of BCCWJ:

  * ひとつひとつ: 604
  * 一つ一つ: 1005
  * 一つひとつ: 293
  * ひとつ一つ: 5

* * *

**EDIT:** This is not limited to 一つひとつ...

  * おそるおそる: 224; 恐る恐る: 193; 恐るおそる: 9; おそる恐る: 0
  * おもいおもい: 2; 思い思い: 183; 思いおもい: 9; おもい思い: 0
  * かさねがさね: 8; 重ね重ね: 24; 重ねがさね: 3; かさね重ね: 0
  * たびたび: 823; 度々: 354; 度たび: 4; たび度: 0

Maybe the users of 度たび／恐るおそる are treating the second part somewhat like a long
okurigana...? I personally do not do this, but it is true that there are
writers who like this style.

