At a glance
Noun のことだから means "knowing (someone)" or "since it's (someone)". The speaker makes a guess or judgment based on what they know about that person's character or habits.
[Noun] のことだから、[guess / judgment]
真面目な田中さんのことだから、きっと遅れないだろう。 Knowing how serious Tanaka is, he surely won't be late.
How to form it
| Attaches to | Example | Register |
|---|---|---|
| Noun (usually a person) | 田中さんのことだから | Neutral |
| Modifier + noun | 真面目な田中さんのことだから | Neutral |
| Noun (polite form) | 田中さんのことですから | Polite |
The second clause usually ends with a guess or judgment, such as だろう, でしょう, はずだ, に違いない or と思う.