The usage of ので etc to leave sentences "hanging"


This is a question I've wanted to ask Japanese natives for a while but have
never gotten the chance. In Japanese there are many more "sentences" that end
unfinished(at least if we are comparing to English). Sometimes these just end
in particles like を、に etc and are very clear(at least to me) as to what is
implied afterwards. Although sometimes I struggle to see exactly what would
come after particles like から、ので etc. How do Japanese natives "think", perhaps
unconsciously, about exchanges like this?

[code]

    「これは？」
    「どうした，サイエ？」
    「いえ、どこからかピンク色の萌え電波受信したので」
    「？」
    
[/code]

Pardon the example but it was the most recent thing I was reading. In this
situation he and サイエ are both on the battlefield and she "picks up" a signal
and then this very brief exchange leaves our friend confused. Now, how does
one actually look at what this ので is doing?

1) Is it used by her to explain to him why she spoke?  
2) Does it have an obvious bit afterwards that is implied (Even if one wasn't
on the battlefield I'm sure one would find that picking up a ピンク色の萌え電波 would
be interesting/surprising)  
3) If it's not one of the above how would a native think about this?




>   1. Is it used by her to explain to him why she spoke?
>   2. Does it have an obvious bit afterwards that is implied
>

Yes, these are the two ways `〜ので。` works. And the more I think about it, it
has a pretty straightforward equivalence to answering a sentence with
`Because…`, and hanging a sentence with `so…`.

## Answering with “Because”

The key in your specific example is that, while `どうした？` is posed as a WHAT
question, it is interpreted and answered as a WHY question.

Suppose you come in early for work and your boss is already there. The boss
can say to you:

  1. どうしてこんな早くに？ (WHY this early?)
  2. どうした、こんな早くに？ (WHAT is the matter, being this early?)
  3. 何してるんだ、こんな早くに？ (WHAT are you doing, this early?)
  4. 早いな。 (You're early.) ← Not even a question

All these can be answered with `眠れなかったので。 (Because I couldn't sleep.)` ,
because you can interpret all such questions/statements as `Why are you this
early`. Note that there is nothing _hanging_ here. You are just answering as
if the boss had asked a WHY question.

At first I thought this might be a typically Japanese “reading between the
lines” mode of communication, but I realized it happens all the time in
English, too. “You're early.” can be responded to with “I couldn't sleep.”
You're answering an implied _why_ question with an implied _because_.

## Hanging with “so…”

This is very similar to hanging a sentence with “so.” There can be a lot of
variance in the length of the hang, and the assertiveness of the whole
sentence.

> 本を買いましたので…… (I bought the book, so…)

Depending on the length of the pause and uncertainty in tone, you may be
fishing for a compliment, waiting for directions on what to do next, or asking
for a reimbursement. The context-sensitivity is just the same as you would
expect in English.

The key here is that you can in fact be quite assertive when ending a sentence
with `so`.

> 本を買いましたので。 (I bought the book, so.)

In this case, all you are _hanging_ for is a simple acknowledgement of your
statement.

