At a glance
～ものだ says that something is natural, expected or proper: "one should", "it is normal that". With the た-form it recalls past habits with nostalgia.
Verb (dictionary form / ない-form) + ものだ
Verb た-form + ものだ (past habits)
約束は守るものだ。 Promises are meant to be kept.
How to form it
| Attaches to | Example | Use |
|---|---|---|
| Verb dictionary form | 守るものだ | What one should do / what is natural |
| Verb ない-form | 忘れないものだ | What one should not do / what naturally doesn't happen |
| Verb た-form | 遊んだものだ | Nostalgic past habit |
| い-adjective | 早いものだ | Feeling about the nature of something |
| な-adjective + な | 不思議なものだ | Feeling about the nature of something |
Register: ものだ is casual or written, ものです is polite, and もんだ is common in conversation.