Grammar Info
N3 Lesson 3: 1/23

なぜなら + から
because, the reason is, that is because

Structure
Casual
Formal
Phrase (A)。なぜなら(ば) + Reason for (A) Phrase + から +
Phrase (A)。なぜなら(ば) + Reason for (A) Phrase + から + です
Details
Register Standard
使用域 一般
Information
When combined with the 接続助詞(せつぞくじょし) (conjunction particle) から, なぜなら (or なぜならば) forms a set pattern that can be translated as ‘why (A), that is because (B)’. Essentially, it is a way to highlight that a ‘because’ is coming at the end of the sentence, drawing attention to it.
なぜなら itself is a 接続詞(せつぞくし) (conjunction) that is a combination of the 副詞(ふくし) (adverb), なぜ ‘why’, and the 仮定形(かていけい) (hypothetical form) of , なら. Literally, なぜなら~から is similar to ‘why is (A) so, (B) is the cause’. This sounds quite dramatic in English, but is a perfectly natural way of emphasizing a statement/fact in Japanese.
To use なぜなら~から, state that fact/important piece of information as (A). Then, at the beginning of a new sentence, なぜなら will be followed by the reason/cause, with から finishing the sentence.
  • 明日(あした)は仕事(しごと)に来(き)ません。なぜなら、明日(あした)は友達(ともだち)結婚式(けっこんしき)に行(い)くからです
    I will not come to work tomorrow. Why? That's because I will be going to my friends' wedding.
  • 卵(たまご)使(つか)わないで作(つく)ってください。なぜなら、私(わたし)は卵(たまご)アレルギーからです
    Please make it without using eggs. Why? because I'm allergic to them.
The primary function of なぜなら in Japanese (as opposed to simply using から or ので by itself) is to gain the attention of the listener, and inform them that important information is coming.
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彼(かれ)は泳(およ)ぎに行(い)けなかった。なぜなら、寒(さむ)かったから
He couldn't go swimming because it was cold.
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すみませんが、正直(しょうじき)に言(い)えないんです。なぜなら、秘密(ひみつ)だから
I'm sorry but I can't tell you truthfully. The reason is that it is a secret.
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彼(かれ)らは来(く)るどうわからないなぜならまだ連絡(れんらく)がきていないからです。
I don't know if they are coming or not because they haven't contacted me yet.
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