Help with "Yappari" and "nai"

[nisenihonjin1400]

What I meant by だ not being a form of です or である is that you cannot simply paste だ everywhere you see a です or である. そうですか cannot be replaced with そうだか because you can't assert something is and then make it a question. I've never heard of い being used as a particle though, I'll have to check up on that. Also, in things like compound sentences, you can't have です anywhere but the end whereas だ can be places other than the end. The sentence そうだと思います cannot also be そうですと思います. If these are the syntactical differences you were talking about, then I guess we were on the same page now.