ものだ
Supposed to, Should, That's the way it is
Structure
［い］Adjective + もの(1) + だ(2)
［な］Adjective + な + もの(1) + だ(2)
(1) もん
(2) ではない、じゃない
Explanation
The word もの, or 物 when written with kanji, functions as a 形式名詞, which is a type of 'dummy noun' in Japanese. It serves a similar role to the English word 'thing' but often refers to more abstract concepts. When もの is used with the auxiliary verb だ, it expresses a general truth or a universally accepted idea. This grammar pattern is commonly used to state what is considered common sense, social norms, or to express a natural, expected outcome of a situation.
To use ものだ, simply add it to the end of a verb or adjective in its attributive form. This structure gives the preceding statement the nuance of being a general principle or a deeply felt observation.
- 学生はよく勉強するものだ。Students are expected to study hard.
- 時間が経つのは本当に速いものだ。Time really does fly, doesn't it?
- 赤ちゃんはよく泣くものだ。It's natural for babies to cry a lot.
This grammar can also express that something is not supposed to happen or goes against common sense. To create the negative form, replace だ with ではない, or its more casual equivalent, じゃない.
- 約束は簡単に破る物ではない。A promise is not something you should break easily.
- 人の悪口を言うものじゃない。You shouldn't speak ill of others.
Caution
In casual conversation, もの is often contracted to もん. This shortened form is primarily used in speech and gives the sentence a more relaxed, informal feel.
- ひとりでここまで来たのか。偉いもんだ。You came all this way by yourself? That's quite an achievement.
- 夜遅くまでゲームをするもんじゃない！You shouldn't play video games late into the night!
Examples
海はしょっぱい物だ。
The sea is supposed to be salty.
学生は真面目な物だ。
Students are supposed to be diligent.
人にうそをつく物じゃない。
You shouldn't lie to people. (not supposed to)
時間は早く過ぎる物だ。
Time tends to pass quickly. (That's just the way it is)
約束は守る物だ。
You're supposed to keep your promises.
手に入らない物ほど欲しくなる物だ。
You always want what you can't have. (That's just the way it is)
借りた物はきちんと返す物だ！
You should properly return things you borrow!
新しいスマホは嬉しい物だ。
A new smartphone is naturally an exciting thing.
人の話は最後まで聞く物だ！
You should listen until the other person has finished speaking!
子供は成長して親から離れていく。家族とはそういう物だ。
Children grow up and leave their parents. That's just what a family is.
勉強は毎日コツコツ続ける物だ。
Studying is something you should do consistently every day. (supposed to)
先生とは生徒を導く物だ。
A teacher is someone who is supposed to guide their students.
長く日本に住んでいると、地震にも慣れる物だ。
When you live in Japan for a long time, you naturally get used to earthquakes. (That's just the way it is)