Dear sensei, I have some questions about the formal form and casual form.
For formal sentences, I could say 車を買います。 And also 車を買うです to make it polite again. George sensei mentioned in the video desu form was as nice as masu form and probably used more. I was still wondering if there was a certain circumstance that one would use a particular form? Is this how would you rank them from most polite to most casual?
車を買います ---> 車を買うです ----> 車を買う ----> 車買う
I guess the "desu" in the "車を買うです" has a different function from the desu in "車です"? Because I always think desu as copula verbs. To me it looks like the verb "buy" and the copula verb are in the same sentence by adding desu at the end. For example, 車を買います = I buy（polite verb） a car. 車です = It is(polite copula verb） a car. 車を買うです = I buy(casual verb) a car is(still a polite copula verb)? or the です here is just being polite and has no meaning. So 車を買うです = I buy(casual verb) a car (just being polite, but not a copula verb).
Does "adding desu at the end to make the sentence polite again" also apply to the desu sentences, or it only applies to sentences with verbs(like buy, go, read...) in them? For example, 犬です。I can say 犬だ to make it casual. Can I say 犬だです to make it polite again?
And here are two strange/weird questions I have :P
Since adding desu at the end make the sentence polite again. For example, 車を買うです is polite. Does 車を買いますです make the sentence super polite or meaningless? If I change it to です to だ (車を買うだ), does this make the sentence super impolite or meaningless?
I am sorry there are so many questions. Thank you for your time. I really appreciate it.
George Sensei's youtube video Hello dear Kanako Sensei, thank you for answering my question. I got pretty much everything. There is just one thing George Sensei mentioned in the video that is little bit different from you were telling me. At the 18:56 part video: https://youtu.be/NRSYkHp7NCc?list=PLOcym2c7xnBwRNLWXOAtlN-9dbLkctxV-, he mentioned that a sentences like "手紙を書かなかったです" or "手紙を書かなかったですか"？ and mentioned those were something Kanako Sensei would say.