～なぜなら（ば）～からだ

Japanese Grammar Advanced Japanese ★★★ 3/5 formal なぜならnazenara(ba) ~ karada
Reading なぜなら
Romaji nazenara(ba) ~ karada
Formation [Statement]. + なぜなら（ば） + [Reason] + からだ / からである

Meaning

A structure used to explicitly introduce a reason for a statement made in the preceding sentence. It translates as 'the reason is that…' or 'this is because…'

なぜなら（ば）～からだ is a two-part structure: なぜなら（ば） opens the explanatory sentence, and からだ closes it. It is used when the speaker wants to clearly and logically justify or explain a previous assertion. The structure is common in essays, presentations, and persuasive writing because it neatly separates the claim from its justification. In spoken Japanese, the shortened form なぜなら is more common than なぜならば. This pattern differs from simply using から because it draws special attention to the explanation. Learners sometimes forget the closing からだ, producing an incomplete sentence. The は in なぜならば is the classical conditional particle, not the topic marker.

Examples

  1. 彼の提案には賛成できない。なぜなら根拠が示されていないからだ。 I cannot agree with his proposal. This is because no evidence has been presented.
  2. この地域の人口は減少し続けている。なぜなら若者が都市部に流出しているからだ。 The population of this area continues to decline. The reason is that young people are migrating to urban areas.
  3. 私は毎朝走ることにしている。なぜなら体力の維持が仕事に不可欠だからだ。 I make it a point to run every morning. This is because maintaining physical fitness is essential for my work.

Usage Guide

Context: written, academic, spoken

Tone: explanatory

Do Say

  • 早期対応が重要だ。なぜなら被害は時間とともに拡大するからだ。
  • その仮説は支持されなかった。なぜなら再現実験で同じ結果が得られなかったからだ。
  • 多言語教育を推進すべきだ。なぜなら国際社会での競争力に直結するからである。

Don't Say

  • なぜなら疲れた。(Omitting からだ at the end — なぜなら must be closed with からだ or からである to complete the structure) → なぜなら疲れたからだ。
  • 遅刻した、なぜなら電車が遅れたからだ。(Inserting なぜなら in the same sentence with a comma — なぜなら begins a new sentence that explains the previous one) → 遅刻した。なぜなら電車が遅れたからだ。

Origin & History

Composed of なぜ (why) and なら（ば） (if/since), literally meaning 'if you ask why.' Combined with からだ (it is because) at the end, the pair frames a clear reason-giving structure.

Cultural Context

Generation: All ages

Social background: Universal

Related Phrases

～あげく（に） An adverb or conjunction meaning 'in the end' or 'after all that,' indicating that after a prolonged effort, deliberation, or struggle, an outcome — typically negative — was reached. ～ことから A phrase that expresses a reason or a cause by presenting an observable fact or characteristic as the basis for a conclusion. It translates roughly as 'from the fact that' or 'because of the fact that.' ～ところから A phrase that introduces the origins or basis of names, theories, ideas, and events. It means 'from the point/aspect that' or 'owing to the fact that.' ～と言うのは A phrase that introduces the reason for what has just been said, meaning 'the reason is' or 'what I mean is.' It bridges a statement to its explanation or justification. ～ばかりに A conjunction meaning 'just because' or 'simply because,' used when a single factor leads to an unfortunate or regrettable outcome. It carries a strong tone of reproach or lament. ～とあって A phrase meaning 'because' or 'given that,' used when the speaker or writer considers the stated reason to be a natural or expected basis for the resulting situation. ～とあっては A conditional phrase meaning 'given that' or 'if it is the case that,' used to indirectly present a factual situation as a reason that makes a particular response unavoidable or natural. ～ばこそ A conjunction that strongly emphasises the reason or cause behind an action or feeling. It conveys 'precisely because' or 'it is exactly because,' stressing that the stated reason is the true and most important one.
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