GRAMMAR
〜ことだから
since it is
knowing (him/her)
Explanation
NOTE
〜ことだから means given that it's X or knowing X (as we do) — used to make an inference based on someone's well-known character or typical behavior.
真面目な彼のことだから、きっと時間通りに来るだろう。
Knowing him (as the serious person he is), he'll surely arrive on time.
The speaker draws a confident guess from the listener's shared knowledge of the person.
NOTE
It typically attaches to nouns referring to people (names, family members, pronouns) and is followed by a prediction about what they will likely do.
NOTE
The second clause often uses expressions of conjecture like 〜だろう, 〜にちがいない, or きっと〜はず.
STRUCTURE
N辞
のことだから田中さんのことだから、きっと明日も遅刻するだろう。
Tanaka-san no koto dakara, kitto ashita mo chikoku suru darou.
Knowing Tanaka-san, he will likely be late again tomorrow.
母のことだから、今ごろ心配して電話をかけているに違いない。
Haha no koto dakara, imagoro shinpai shite denwa o kakete iru ni chigai nai.
Since it's my mother, she must be worrying and calling me right about now.
彼のことだから、この仕事も完璧にやり遂げるはずだ。
Kare no koto dakara, kono shigoto mo kanpeki ni yaritogeru hazu da.
Knowing him, he will surely complete this job perfectly as well.
田中さんのことだから、もう準備を終えているだろう。
Tanaka-san no koto dakara, mou junbi o oete iru darou.
Knowing Tanaka-san, he has probably already finished the preparations.
優しい母のことだから、きっと許してくれるはずだ。
Yasashii haha no koto dakara, kitto yurushite kureru hazu da.
Given that it's my kind mother, she'll surely forgive me.
忘れっぽい弟のことだから、また傘を無くしたにちがいない。
Wasureppoi otouto no koto dakara, mata kasa o nakushita ni chigainai.
Knowing my forgetful little brother, he must have lost his umbrella again.
Practice exercises
1
彼女のことだから、時間には厳しいものだから、遅れないように。
Knowing her, since she is strict about time, make sure not to be late.
Answer
ことだから
2
彼のことだから、責任感が強いばかりに一人で抱え込んでしまうだろう。
Knowing him, he will probably take on everything by himself simply because he has a strong sense of responsibility.
Answer
ことだから
3
部長のことだから、少しの失敗は気にしないものだから安心していいよ。
Knowing our manager, since he doesn't mind small mistakes, you can rest assured.
Answer
ことだから
4
日本の会社のことだから、残業が多いのは仕方ない。
Since it's a Japanese company, it can't be helped that there's a lot of overtime.
Answer
ことだから
5
日本の伝統文化のことだから、細部まで美意識が宿っているはずだ。
Knowing Japanese traditional culture, an aesthetic sense must reside even in the smallest details.
Answer
ことだから