fukuhara: Perhaps it's wiser to state what I really have in mind rather than try to implicitly make native speakers confirm or reject it:

The tag question must be based on the main verb in the statement and must agree with the subject of the main verb as well, right?

In 1, there's no problem. I know that. But 3, grammatically speaking, is quite parallel with 1. So, again, grammatically speaking, 3 should be well-formed. However, it seems semantically speaking, it sounds odd.

2, on the other hand, seems to be grammatically wrong, at least as far as my knowledge of grammar says. But it seems to be OK to native speakers despite the fact that the tag question is based not on the main verb and its subject, but on the verb used in the embedded clause and its subject.

In other words, I want native speakers to tell me if a tag question can be based on the embedded clauses or not. Here are more examples which may help:


(For the sake of semantic problems, I won't use 'I' to start my sentences)

Statement: He knows you know she went out last night,....?


Possible tag questions:

1) doesn't he?
2) don't you?
3) didn't she?

(My knowledge says only number 1 is OK)

But, if I change the 'he' at the beginning of my statement with 'I', it seems things change:

Statement: I know you know she went out out last night, ...?

1) don't I?
2) don't you?
3) didn't she?

Here, it seems, based on the replies I got, that strikingly number 2 is OK, while nothing has really changed compared with the previous example.

I want natives to comment on my assumptions, please. Just tell me if they sound OK or not. Thanks in advance.