How is this で being used as a question marker?


From からかい上手の高木さん episode 1 高木 is pulling a prank on 西方 while borrowing his
eraser, in which she starts to convince him that he wrote his crush’s name on
his eraser; thus it makes him believe that his crush’s identity has been
exposed to 高木. 西方 now starting to think that he may have wrote a name on his
eraser after all (but still in somewhat doubt), then says to himself (at 6min
13sec): 書いたのか？ 書いたのか？俺！ 忘れてるだけ **で** … For the last clause listed, in the
English subtitles it translates to, ”Am I just forgetting?” I have been having
trouble with the で placed at the end there. So far my best guess is that is
some sort of informal contraction of ではないか; as in: 忘れてるだけではないか = “Is it that
(I am) just forgetting?” Any help towards an understanding for this would be
much appreciated. Thanks.




I think you could interpret it in two ways.

It could be the TE FORM of the copula. Therefore:

I am just forgetting **and**... (that's bad)

Or as the function of the TE particle that expresses the method:

**By** only forgetting ... (my secret will be exposed).

I really don't think it is abbreviated.




I think you could interpret it in two ways.

It could be the TE FORM of the copula. Therefore:

I am just forgetting **and**... (that's bad)

Or as the function of the TE particle that expresses the method:

**By** only forgetting ... (my secret will be exposed).

I really don't think it is abbreviated.

