copula N4 common casualpolitewritten
〜は〜の一つだ — ~ is one of the ~
〜は〜の一つだ ・ はのひとつだ
Meaning
- X is one of the Y — presents X as a single member of a larger category Y
Key sentence
富士山は日本の象徴の一つだ。
Mt. Fuji is one of Japan's symbols.
Formation
| Attaches to | Form | Example |
|---|---|---|
| X は + Y の一つだ | X は Y の一つだ | これは原因の一つだ (this is one of the causes) |
Examples
読書は私の趣味の一つです。
Reading is one of my hobbies.
その事故は今年最大のニュースの一つだった。
That accident was one of the biggest news stories this year.
When you can't use it
- Y names a set or category (it carries a plural sense), and 〜の一つ marks X as just one member among several — so it pairs naturally with 'one of the most ~' phrasing (最も〜なものの一つ).
Notes
- For people, swap the counter: 〜の一人だ (彼は候補者の一人だ = 'he's one of the candidates'). The counter follows whatever is being counted.
See 〜は〜の一つだ in real sentences
Jengo shows 〜は〜の一つだ the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled from published Japanese grammar references.