事だから
It is exactly because
Structure
Noun + の + ことだから
［な］Adjective + な + ことだから
Explanation
The phrase ことだから is used when the speaker makes a confident conclusion about (B) based on their specific knowledge of (A). It's frequently translated as 'knowing (A), it's no surprise that (B)' or 'since it's (A), then of course (B)'. Grammatically, ことだから is formed from the noun こと ('the fact that'), the copula だ, and the reason-marking particle から. This literally suggests 'from the fact that it is (A), (B) follows'. This structure implies that since (A) is a known truth, (B) is a logical and expected outcome.
In cases where a prediction is being made, ことだから typically follows a noun with の or a verb in its plain form. When used with a noun, it very often refers to a person with whom the speaker is well-acquainted.
- 真面目な山田さんのことだから、きっと時間どおりに来るだろう。Knowing how diligent Yamada-san is, he will surely be here on time.
- 甘いものが好きな妹のことだから、このケーキも喜んでくれるはずだ。Given that it's my little sister who loves sweets, she is bound to be delighted with this cake.
Another use of ことだから is to frame situation (A) as an ideal chance to do (B). In this usage, it can follow verbs in their various standard forms, as judged by the speaker.
- こんなに天気が良いことだから、公園に散歩にでも行かない？Since the weather is this nice, why don't we go for a walk in the park or something?
- プロジェクトが成功したことだから、みんなで祝いましょう。Now that the project has succeeded, let's all celebrate together.
Finally, ことだから can be used to simply present (A) as a strong reason for (B). When used this way, it may be preceded by verbs in their standard forms, nouns followed by の, or な-adjectives followed by な.
- これは安全に関わる大切なことなので、ルールをしっかり守ってください。As this is an important matter concerning safety, please be sure to follow the rules.
- 大事なテストのことだから、今夜は徹夜で勉強するつもりだ。Because it's such an important test, I'm planning to study all night tonight.
Even with these three distinct nuances, the speaker's exact intention is generally obvious from the context provided in part (B) of the sentence. For this reason, you can think of ことだから as fundamentally meaning 'based on the nature of (A), (B) is a natural conclusion'.
Examples
母のことだから、きっとおいしい料理を作ってくれるでしょう。
It is exactly because it's my mother that I'm sure she'll make us a delicious meal.
頑張り屋の田中さんのことだから、この仕事もやり遂げるだろう。
It is exactly because we're talking about the hardworking Tanaka-san that he will likely see this job through to the end.
彼はまだ初心者ということだから、少しのミスは大目に見てあげよう。
It is exactly because he's still a beginner that we should overlook his minor mistakes.
明日は雨が降るということだから、傘を持っていきなさい。
It is exactly because it's going to rain tomorrow that you should take an umbrella with you.
ここは撮影禁止ということだから、カメラはしまってください。
It is exactly because photography is prohibited here that you must put your camera away.
それは非常に専門的なことだから、素人の私にはわからない。
It is exactly because that is a highly specialized topic that an amateur like me wouldn't understand.
約束を守らない彼のことだから、また遅刻するだろう。
It is exactly because he's someone who never keeps his promises that he'll probably be late again.
先生が「大丈夫だ」とのことだから、安心して帰った。
It is exactly because the doctor said, "It's alright," that I went home feeling relieved.
最近とても忙しいということだから、無理をしないでくださいね。
It is exactly because I hear you've been very busy lately that I want to tell you not to overdo it.
まだ小さい子供のことだから、仕方がないですよ。
It is exactly because they are still little kids that it can't be helped.
今回は特別な場合ということだから、許可された。
It is exactly because this is a special case that permission was granted.
そういう訳ということだから、この計画は中止になった。
It is exactly because those are the circumstances that this plan has been canceled.