N2 — outside your level filter

ことだから

ことだからkoto da karaN2neutral

のことだから

knowing X as we do — a prediction from someone's known character

あの人ひとのことだから、また忘わすれてるんじゃない？

ano hito no koto da kara, mata wasureteru n ja nai?

Knowing him, he's probably forgotten again, don't you think? casual

時間じかんに厳きびしい先生せんせいのことだから、もう着ついているでしょう。

jikan ni kibishii sensei no koto da kara, mou tsuite iru deshou.

He's bound to be there already, knowing the teacher — a stickler for time if ever there was one. neutral

Same meaning13

because; the reason is

ばかりにall because — one small thing cost far more than it shouldattaches at
だってcasual reason-opener ('cause, X); casual "even N"attaches at
からこそprecisely because — this reason and no other made it happenattaches at
からbecause; so — the speaker's own reasonattaches at
ものだからbecause — offered as an excuse the speaker could not helpattaches at
もの'cause; but I — a reason fired back at the listenerattaches at
んですit's that…; you see — marks the sentence as an explanationattaches at
なくてnot… and; because (one) doesn'tattaches at
なぜならthe reason is; because — opens a new sentence explaining the last oneattaches at
につきowing to N; per N (formal, written)attaches at
のでbecause; since — reason as circumstanceattaches at
せいかperhaps because; maybe it's because — the cause offered only as a guessattaches at
しand what's more — listing reasonsattaches at

All examples3

knowing X — predicts what they'll do, based on their character

あの人ひとのことだから、また忘わすれてるんじゃない？
ano hito no koto da kara, mata wasureteru n ja nai?
Knowing him, he's probably forgotten again, don't you think? casual
時間じかんに厳きびしい先生せんせいのことだから、もう着ついているでしょう。
jikan ni kibishii sensei no koto da kara, mou tsuite iru deshou.
He's bound to be there already, knowing the teacher — a stickler for time if ever there was one. neutral
几帳面きちょうめんな部長ぶちょうのことですから、資料しりょうはもうご用意よういなさっているはずです。
kichoumen na buchou no koto desu kara, shiryou wa mou go youi nasatte iru hazu desu.
The director being as meticulous as he is, he will surely have the materials ready. formal

How it's formed1

All forms1

politeのことですからnokotodesukara

Notes

The ending must be a guess, like きっと〜だろう. A plain fact instead
(×彼かれのことだから遅おくれました) doesn't work here.