The usage of ので etc to leave sentences "hanging"

Question

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?

「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」
「？」

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?

Answer 1

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.

Answer 2

In Japanese there are many more "sentences" that end unfinished(at least if we are comparing to English)

This is my speculation (as a native), but I think this might be because saying a clear opinion can be considered offensive, inconsiderate or non-woman-like.

An example would be:

「この車にしたらどうだね、君」
「こちらは少々値が張るようですので。。。」(違う車にしたいです)

Of course it could be just because it's convenient.

「お前ラーメン買ってこいよ」
「いや腹減ったのお前だから」（お前が買ってこいよ）

As for your example I think it's just the later. As in （さっき「これは？」といったのは）「...電波を受信したので」（です）