Is it possible to use 丁寧語 before verbs that use a quoting particle?


犬かどうか分からない・犬ですかどうか分からない

きっと行くと言っていました・きっと行きますと言っていました

いい大学だと思う・いい大学ですと思う

Can't find a passage in the textbook that mentions and I'm not sure where to
look. I feel like I've definitely heard something of the sort before.




Your first example is not a quote but an [embedded
question](https://japanese.stackexchange.com/a/13038/5010). です is never used
in an embedded question. For example, you can never say ❌駅がどこにありますか知っていますか or
❌誰ですか分からない.

If you are clearly quoting someone else's statement verbatim (i.e., [direct
speech](https://japanese.stackexchange.com/q/30584/5010)), the quote can
contain whatever that was actually said, including です or any other keigo. In
indirect speech, です/ます is generally not used inside a quote.

  * 彼女は「やります」と言っていました。  
彼女はやりますと言っていました。  
She was saying "I'll do it".

  * 彼女はやると言っていました。  
She was saying she would do it.

The distinction between the two is not always clear in Japanese because
subjects are usually omitted, and quotation marks are optional even with
direct speech. Still, if you hear です/ます in a quote, you can tell it's a
verbatim quote.

Thus, いい大学ですと思う almost always sounds odd because most people don't use polite
language when they think something in their mind or when they speak to
themself. An extremely elegant character in fiction (e.g., a young innocent
princess) may use polite language even in monologues, in which case
いい大学ですと思いました could be fine, but this is fairly exceptional.

