Uses of に思う in this statement


> 俺が疑問に思った一名の欠員について、皆も何かしら不審に思う点があるらしい。

For 疑問に思った does ["〜に思うこと is equivalent to
〜に対して思うこと."](https://japanese.stackexchange.com/questions/29619/trouble-
interpreting-%e3%81%ab%e6%80%9d%e3%81%86-in-%e3%81%9d%e3%81%ae%e6%ad%a6%e5%85%b7%e3%81%ab%e6%80%9d%e3%81%86%e3%81%93%e3%81%a8%e3%81%af%e3%81%84%e3%81%a3%e3%81%b1%e3%81%84%e3%81%82%e3%82%8b%e3%81%bf%e3%81%9f%e3%81%84)
apply? Or is it 疑問と思った?

For 不審に思う, is it mandatory to read it as the adverbial of 不審, or do you
interpret it the same as 疑問に思った?




The two structures are very similar in meaning, however:

With (〜が)〜だと思う you're stating that you think/feel (something) **is** a certain
way.

With (〜を)〜に思う you're stating **how** you think/feel (about something).

So 疑問だと思う means "I think/feel (something) is a question".

But 疑問に思う means "I feel dubiously about (something)".

Likewise:

不審だと思う means "I think/feel (something) is suspicious".

But 不審に思う means "I feel suspiciously about (something)".




XXを疑問/不審に思う means "feel dubious about XX" "feel suspicious about XX", i.e.
"feel that XX is questionable" "feel that XX is suspicious".

> 一名の欠員を疑問に思う I feel dubious about one vacancy  
>  (≂ ～～をおかしいと思う/疑わしいと思う)  
>  その点を不審に思う They feel suspicious about that point  
>  (≂ ～～を変だと思う/怪しいと思う)

Similar examples:

> ～～を残念に思う feel sad about ~~ / feel that ~~ is unfortunate  
>  ～～を変に思う feel ~~ is strange

疑問に, 不審に, 残念に etc. here are adverbial forms, but they're not describing how
the action 思う is performed, but describing what you feel/think the object (the
thing marked with を) is.

For more, please refer to: [Confusion with に、を、と particles used with verbs
like 感じる](https://japanese.stackexchange.com/a/57223/9831)

* * *

So to answer your questions:

> For 疑問に思った does "〜に思うこと is equivalent to 〜に対して思うこと." apply? Or is it 疑問と思った?

The に in that thread has a different usage/meaning. 疑問と思った is close, but
疑問だと思った might sound a bit more natural.

> For 不審に思う, is it mandatory to read it as the adverbial of 不審, or do you
> interpret it the same as 疑問に思った?

The latter.

