why is the reading of 瞬く and 瞬き not the same?


Out of sheer curiosity I was wondering why 瞬く is read as またたく but 瞬き is read
as まばたき.




>   1. （A）まばたくー （B）まばたき
>   2. （A）またたくー （B）またたき
>

>
> where (A) is a verb and (B) is a noun.

I think that the use of these words depends on the generation and the dialect
very much, therefore what is written from now on is my personal opinion.

Generally group 1 is used to describe the blink of eyes, on the other hand
group 2 is used to describe the fluctuation of emitted light from objects such
as stars, fishing boat equipped with fishing lamps, candles, etc.

As the Japanese word for the set phrase "in a very short time", またたくまに is used
but まばたくまに is not.

As for しばたく/しばたたく and しばたき/しばたたき which are described in broccoli forest's
answer, I have rarely said or heard them said; a very little use frequency of
them is also written in the follow-up survey in the answer.

**The etymology**

The verb _matataku_ (瞬｛またた｝く) is made of _ma_ and _tataku_ (叩{たた}く) where _ma_
means eye (目{め}) and _tataku_ (叩{たた}く) means to strike, so _matataku_
(瞬{またた}く) literally means to strike eyes (with eyelids), then _matataku_
(瞬{またた}く) means to blink eyes. As for _mabataku_ (瞬{まばた}く), ma means _me_
(目{め}), and _bataku_ is an euphonic change from _hataku_ (叩{はた}く) which means
strike. Therefore _matataku_ (瞬{またた}く) and _mabataku_ (瞬{まばた}く) have the
almost same origin derived from the same motion of blinking eyes.

On the other hand, _shibataku_ (しばたく) has different etymology; it is derived
from _shiba_ (しば) and _tataku_ (叩{たた}く). _shiba_ (しば) is abbreviated from
_shibashiba_ (屡/屢{しばしば}) which is an adverb meaning often or many times. Hence
the whole meaning of _shibatataku_ (しばたたく) is to strike often. Originally
_shibatataku_ (しばたたく) was used as the phrase " _me wo sibashiba tatataku_
(目{め}をしばしば叩{たた}く)" which means to strike eyes often (with eyelids).

So if we trace the word, we found out that the original phrase gradually
turned to the present form as:  
" _me wo shibashiba tataku_ " → " _shibashiba tataku_ " → " _shiba tataku_ " →
" _shibataku_ " → (it becomes nearly an obsolete word now.)

* * *

I'll show you the intonations of the words in the following illustration.
Before that the rules of accent or intonation of a Japanese word are like:

> 1) Accent is relative emphasis or prominence given to a certain syllable in
> a word.  
>  2) Intonation is a pattern of rise and fall in the level/pitch of the
> voice.  
>  3) Emphasis is produced through pitch alone, so it is called pitch accent.  
>  4) Largely, words are divided into two groups whether there is an accent or
> not.  
>  5) The accent given to the emphasized syllable is called an accent nucleus.  
>  6) Pitch falls after the accent nucleus.  
>  7) Unless the first syllable is an accent nucleus, there is a rise of pitch
> after the first syllable of a word.

I'll show you how the intonation lines written in red in the illustration are
decided by the rules.  
As for まばたく, we give an accent to た which is called an accent nucleus by the
rule 5), so by the rule 6) the pitch becomes to fall from た to く, then the
intonation around たく becomes like まば[たく]{HL}. And by the rule 7) the
intonation around まば becomes like [まば]{LH}たく, so the whole intonation becomes
[まばたく]{LHHL}.

As for accent nucleus, ば in まばたき and the second た in またたく become the accent
nucleus of each word, and またたき has not it. And after applying the rule 6) and
the rule 7) to these words, each intonation becomes like this respectively.  
[まばたき]{LHLL}, [またたく]{LHHL} and [またたき]{LHHH}

[![enter image description
here](https://i.stack.imgur.com/D1Clu.jpg)](https://i.stack.imgur.com/D1Clu.jpg)




> 瞬く is read as またたく but 瞬き is read as まばたき

is an over-simplification.

瞬く has three (or four) possible kun'yomi.

  * [またたく](https://dictionary.goo.ne.jp/jn/208303/meaning/m0u/): _[eyes] blink (once); [light sources] turn on and off or pulsate (e.g. blink, twinkle, flicker...)_
  * [まばたく](https://dictionary.goo.ne.jp/jn/209365/meaning/m0u/): _[eyes] blink (once)_
  * [しばたたく](https://dictionary.goo.ne.jp/jn/99886/meaning/m0u/): _[eyes] blink (rapidly in a row); blink (in surprise) at_
  * [しばたく](https://dictionary.goo.ne.jp/jn/99880/meaning/m0u/): variant of しばたたく

Thus, the nominalized form 瞬き also has as many readings.

  * またたき
  * まばたき
  * しばたたき
  * しばたき

The interesting fact is that, noun forms are ranked by frequency as:

> **まばたき** > またたき > しばたき >= しばたたく

while verb forms are:

> またたく > **まばたく** > しばたく >= しばたたく

Why this happens? Undoubtedly まばたき is the most common word for "eye blink",
but the verb まばたく is not a very useful word in modern Japanese, because it
means " _an eye_ blinks" (see above) rather than " _a person_ blinks (their
eyes)". For the latter meaning we say まばたき（を）する, and this is a fairly common
phrase.

In this sense, you might expect 瞬く more _likely_ to be read またたく, and 瞬き more
_likely_ まばたき, but they are by no means the only reading of the each.

> 星の瞬（またた）き _twinkling of stars_

* * *

**Follow-up**

Below is the frequencies each word form appears in the
[BCCWJ](http://pj.ninjal.ac.jp/corpus_center/bccwj/en/) corpus.

  * **nouns**

    * またたき: ≥ 38*
    * まばたき: ≤ 384*
    * しばたたき + しばたき: ≥ 0  
* The raw results of まばたき was 398, but contains at least 14 obvious mistagging for またたき or perhaps しばたたき (due to homography).
  * **dictionary forms**

    * またたく: ≥ 350† (an idiom 瞬【またた】く間【ま】に takes up around 80%)
    * まばたく: ≥ 4†
    * しばたたく + しばたく: ≤ 8†  
† The raw results of しばたたく was 183, but contains at least 174 obvious
mistagging for またたく or まばたく and 1 mistokenization.

  * **causatives**

    * またたかせる: 4 ± 2‡
    * まばたかせる: 3 ± 2‡
    * しばたたかせる + しばたかせる: ≤ 54‡  
‡ Again, 3 possible mistagging for またたく or まばたく.

So you might also expect 瞬かせる to be read しばた（た）かせる, if you want.

