"If you were to ask why, ..."

Question

In English, we have a construction like

Yeah, I would never let him in. If you were to ask why, well, I guess I'd say because he's too young.

My sense of the nuance is that it admits that what you just said may result in a "why?"; that what you said is perhaps a little hard to understand without a reason. Sort of a way of softening a strong statement. (The "guess" softens it even more in that example.)

I was trying to think of an equivalent in Japanese, and first, I thought of 「なぜなら」, but that seems to have a completely different nuance to me (rather stilted, and certainly not softening; perhaps like "As to why," in English).

Then, I thought of perhaps the more syntactically similar option, 「なぜかというと」. I think this might have a similar softening nuance to "If you were to ask why", but I'm not entirely sure since I don't hear it too often.

Is 「なぜかというと、〜」 a reasonable equivalent to "If you were to ask why, ..." in English (i.e., similar nuance)? Is there a better equivalent?

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英語では、こういう表現があります：

Yeah, I would never let him in. If you were to ask why, well, I guess I'd say because he's too young.

この表現は、「なぜ？」と思われるだろうな、理由をつけないと分かりづらいだろうなと思っているということを伝えるようなニュアンスがあると思います。強い言い方を和らげるような使い方があると。（この例文は、"guess"によって更に和らげられていますね。）

日本語で言おうとして、最初に頭に浮かんだのは「なぜなら」だったのですが、「なぜなら」は全く違うニュアンスを持っているような気がします。（とても堅苦しい、けして和らげはしないニュアンス。英語の"As to why,"に似てるような。）

次に思いついたのは、「なぜかというと」だったのです。考えてみるとこの方が構文的には英語に近いですね。"If you were to ask why"と同じ和らげるニュアンスがあるような気がしますが、あまり耳にしない表現なので、よく分かりません。

「なぜかというと、〜」は"If you were to ask why"に相当する日本語ですか？更に相当する日本語はありますか？

Answer 1

I agree with your statement regarding 「なぜなら」. That is not the softener you want to put in your washer because it gives off an almost clinical or mathematical coldness. = "A is B because ~~."

「なぜかというと」 does sound softer and so does 「なぜかといえば」, but I have to wonder if we would use 「なぜ」 when we wanted to sound soft. 「なぜ」 in and itself could sound kind of cold, too, if I were to speak on the native level.

My personal recommendation, thus, might be 「というのは」 or 「というのも」, which is even softer than the two above because of the lack of the word 「なぜ」.　Every native speaker knows that you are going to give a reason if you use one of those two phrases.

Colloquially, that would be 「つーのは」, which I am sure someone in your calibre would be familiar with.

「というのは/というのも、あの[子]{こ}は[歳]{とし}が[若]{わか}すぎるんですよね。」