Sentence topic without grammatical function


From
[here](https://www3.nhk.or.jp/news/easy/k10011595251000/k10011595251000.html):

> このスポーツは、海の上を走る水上オートバイから足に付けたボードにホースで水を送って、ボードから出る水の強い力で空中を飛びます。  
>  **In** this sport you fly through the air using the force of water ejected
> from a board attached to the feet. Water is sent to the board using a hose
> from a jet ski that runs along the surface of the sea. ( _Wow. I couldn't
> get that into just one English sentence._ )

Sometimes I see a sentence where the topic appears to serve no grammatical
function in the rest of the sentence. This seems to be one of those cases.
Normally the topic serves as the subject or object of one of the verbs in the
sentence, or sometimes it can be adverbial.

In my English translation I used " **In** this sport" so that the topic
adverbially acts on 飛ぶ. If I'd tried to write this sentence in Japanese I'd
similarly have begun with このスポーツ **で** は. Would I be wrong to do that? Am I
missing something in the way I think about topics?




Since this is in a formal article, I personally think this is a poorly-written
sentence that has a subject-predicate mismatch. It should have been either of
the following:

  * このスポーツ **は** 、(略)水の力で空中を飛ぶ **ものです** 。
  * このスポーツ **では** 、(略)水の力で空中を飛びます。

Japanese is a topic-prominent language, and sometimes このスポーツは空中を飛びます can be
perfectly acceptable as an _eel sentence_ , particularly in speech. For
example it's perfectly fine to say
ウェイクボードはジャンプするだけですが[フライボード](https://en.wikipedia.org/wiki/Flyboard)は空中を飛びます.
For details, please see
[this](https://japanese.stackexchange.com/q/48986/5010) and
[this](https://japanese.stackexchange.com/q/44053/5010). That said, I believe
eel sentences should be avoided when you formally describe a complex idea and
there is no contrast nor repetition.

* * *

Admittedly, there are a few native speakers who do this even in formal
situations, so the level of acceptance may vary.

  * (questionable) 最大の問題は予算がありません。
  * (good) 最大の問題は予算がないことです。／最大の問題として予算がありません。
  * (questionable) 原因は、日付をよく確認しませんでした。
  * (good) 原因は、日付をよく確認しなかったことです。




Since this is in a formal article, I personally think this is a poorly-written
sentence that has a subject-predicate mismatch. It should have been either of
the following:

  * このスポーツ **は** 、(略)水の力で空中を飛ぶ **ものです** 。
  * このスポーツ **では** 、(略)水の力で空中を飛びます。

Japanese is a topic-prominent language, and sometimes このスポーツは空中を飛びます can be
perfectly acceptable as an _eel sentence_ , particularly in speech. For
example it's perfectly fine to say
ウェイクボードはジャンプするだけですが[フライボード](https://en.wikipedia.org/wiki/Flyboard)は空中を飛びます.
For details, please see
[this](https://japanese.stackexchange.com/q/48986/5010) and
[this](https://japanese.stackexchange.com/q/44053/5010). That said, I believe
eel sentences should be avoided when you formally describe a complex idea and
there is no contrast nor repetition.

* * *

Admittedly, there are a few native speakers who do this even in formal
situations, so the level of acceptance may vary.

  * (questionable) 最大の問題は予算がありません。
  * (good) 最大の問題は予算がないことです。／最大の問題として予算がありません。
  * (questionable) 原因は、日付をよく確認しませんでした。
  * (good) 原因は、日付をよく確認しなかったことです。

