Isn't it ?

FelixxxIf I say " I think it is really a great idea. "Are Both "Don't I" ," Isn't it" ok?

As tags, the first sounds illogical and the second sounds meaningless. I can't see that the sentence, since it begins with 'I think', can accept any standard tag question, though it could take other tags:

I think it's really a great idea, OK?
I thi

"OK" in what sense? Do you mean as tag questions spoken by the same person?

"I think it is really a great idea, don't I?"
"I think it is really a great idea, isn't it?"

The first one of these seems unusual. Usually you don't ask someone else to confirm what you think.

If you say, "I think it's really a great idea!", then you can follow this with, "Isn't it?" - that is, you're asking confirmation from the listener, "Don't you think it's a great idea too?" "Don't I?" would not be correct here.

"Don't I?" would be used, for example, in the following situation: "I think I look great in this new dress! Don't I?" - that is, you're asking confirmation from

Thanks brothers! Understood

FelixxxI think it is really a great idea, don't I?

This doesn't make sense unless you don't know what you think. Why would you ask someone else what you think? More likely you don't know what someone else thinks:

You think it's really a great idea, don't you?

isn't it doesn't work in either case.

CJ

I think that "I think it's really a great idea ... isn't it?" (one could debate how to punctuate it) is acceptable in ordinary conversation, even though it may not be a perfectly logically formed tag question.