Using です inside an indirect quote


In the sentence "そう **です** と思います", is です making the sentence grammatically
incorrect? If so, why not in the sentence "「そうです」と言った" making it incorrect?
Thanks in advance! Isn't it like "I think it probably is so." in a very very
humble way?




Generally, です/ます before と is allowed when you use [direct
speech](http://www.studyandexam.com/direct-indirect-speech.html), i.e., when
you quote someone's statement without changing it. Note that, however,
brackets are optional in Japanese even when you use direct speech, as long as
who said it was clear from the context or the choice of personal pronouns. The
following sentences are all fine.

>   * 彼女は「あなたが好きです」と言った。  
>  She said "I love you." (typical _direct_ speech)
>   * 彼女はあなたが好きですと言った。  
>  She said "I love you." ( _direct_ speech with brackets omitted)
>   * 彼女は俺が好きだと言った。  
>  She said she loves me. (typical _indirect_ speech; です should not be used)
>

Likewise, そうですと言った (without brackets) is totally fine if someone actually said
そうです out loud.

Next, you cannot directly quote someone's thoughts, and you don't use polite
form when you think something within yourself. This means you should not use
ます/です with 思う/考える/etc regardless of who thought it, and regardless of whether
there are brackets. A rule of thumb is that "～ますと思う" and "～ですと思う" are almost
always incorrect. As a rare exception, if you really feel you "said" something
within yourself, ～ですと may appear.

>   * 心の中で、お金持ちになりたいですと神様に願った。  
>  I prayed to God within myself, "I want to be rich, please".
>

