Why is it that the っけ suffix  can only be attached to a question-sentence


Why is it that the っけ suffix / け particle (indicating that the speaker is
trying to recall some information) can only be attached to a sentence when the
sentence itself is a question-sentence?

Because all 10 example usages i see in
[WWWJDIC](http://www.csse.monash.edu.au/~jwb/cgi-
bin/wwwjdic.cgi?1MUE%E3%81%A3%E3%81%91) does that, hence the question.




Although these sentences are nearly always _translated_ as questions, the
(admittedly informal and possibly colloquial) usage of っけ followed by か
suggests that there is a difference at least on some level. In my experience,
"questions" formed via the っけ particle are often rhetorical -- but just as
often, they are interpreted as a request for information.

Basically though, the answer is **yes, use of っけ to indicate an attempt to
recall information pretty much always turns the sentence into a question.**

**Edit:** Although I believe that this is implicit in my original answer
above, I though I would more explicitly answer your question post-edit.

It is not so much that っけ can _only be used_ with questions, but rather that
it _turns sentences it **is** used with **into** a question._ For example,
consider the following:

>   * あなたの名前は何ですか。
>   * あなたの名前は何でしたっけ。 (warning: this is probably a _bit_ rude.)
>

This is an example of っけ being used on a sentence that is a question-form
(i.e. it uses an interrogative, in this case 何); but it doesn't **have** to
be, as in the following examples.

>   * ここはオハイオ州です。
>   * ここはオハイオ州でしたっけ。
>

In these sentences, っけ is indicating that the speaker cannot recall what state
he or she is in; by saying this, he or she is **implicitly** requesting the
listener supply that information, which is to say that っけ is _turning the
sentence **into** a question_




Although these sentences are nearly always _translated_ as questions, the
(admittedly informal and possibly colloquial) usage of っけ followed by か
suggests that there is a difference at least on some level. In my experience,
"questions" formed via the っけ particle are often rhetorical -- but just as
often, they are interpreted as a request for information.

Basically though, the answer is **yes, use of っけ to indicate an attempt to
recall information pretty much always turns the sentence into a question.**

**Edit:** Although I believe that this is implicit in my original answer
above, I though I would more explicitly answer your question post-edit.

It is not so much that っけ can _only be used_ with questions, but rather that
it _turns sentences it **is** used with **into** a question._ For example,
consider the following:

>   * あなたの名前は何ですか。
>   * あなたの名前は何でしたっけ。 (warning: this is probably a _bit_ rude.)
>

This is an example of っけ being used on a sentence that is a question-form
(i.e. it uses an interrogative, in this case 何); but it doesn't **have** to
be, as in the following examples.

>   * ここはオハイオ州です。
>   * ここはオハイオ州でしたっけ。
>

In these sentences, っけ is indicating that the speaker cannot recall what state
he or she is in; by saying this, he or she is **implicitly** requesting the
listener supply that information, which is to say that っけ is _turning the
sentence **into** a question_

