なぜなら + から
Because, The reason is, That is because
Structure
Explanation
When used in conjunction with the particle から, なぜなら (or its more formal version なぜならば) forms a set expression that can be translated as 'The reason for (A) is that (B)'. This structure is a way of signaling that a reason will be given at the end of the sentence, drawing the listener's attention to it.
なぜなら is itself a conjunction, created by combining the adverb なぜ ('why') and なら, which is the hypothetical form of だ. A literal interpretation of なぜなら～から is 'if you ask why (A), it's because of (B)'. While this might sound somewhat stiff in English, it is a very natural way to put emphasis on a reason in Japanese.
To correctly use なぜなら～から, you first present a statement or piece of information as (A). Then, in a new sentence, なぜなら introduces the reason, which is then concluded with から to mark it as the cause.
- このケーキは食べられません。なぜなら、ダイエット中だからです。I can't eat this cake. That's because I'm on a diet.
- 今日は早く帰りたいです。なぜなら、頭が痛いからです。I'd like to go home early today. The reason is because my head hurts.
The main purpose of using なぜなら in Japanese, instead of simply relying on から or ので alone, is to alert the listener and let them know that an important explanation will follow.
Examples
このケーキは食べられません。なぜなら、ダイエット中だからです。
I can't eat this cake. Why? Because I'm on a diet.
今日はとても眠い。なぜなら、昨日の夜あまり寝ていないから。
I'm very sleepy today because I didn't get much sleep last night.
この部屋は静かだ。なぜなら、だれもいないからです。
This room is quiet. The reason is that nobody is here.
引っ越しをしたいです。なぜなら、今の家は狭いから。
I want to move. Why? Because my current house is too small.
パーティーには行きませんでした。なぜなら、頭が痛かったからです。
I didn't go to the party because I had a headache.
私は夏が好きです。なぜなら、海に行けるから。
I like summer. Why? Because I can go to the beach.
エアコンをつけてください。なぜなら、とても暑いからです。
Please turn on the air conditioner. The reason is that it's very hot.
急がなければなりません。なぜなら、約束の時間に遅れてしまうから。
I have to hurry. Why? Because I'll be late for my appointment.
彼は人気がある。なぜなら、親切で面白いから。
He's popular. Why? Because he is kind and interesting.
このレストランはいつも込んでいます。なぜなら、安くておいしいからです。
This restaurant is always crowded because the food is cheap and delicious.
この漢字は読めません。なぜなら、まだ習っていないからです。
I can't read this kanji. The reason is that I haven't learned it yet.
今日はうれしいです。なぜなら、友達からプレゼントをもらったから。
I'm happy today. Why? Because I got a present from my friend.