のは～だIdentifying the missing detail
This pattern presents a whole situation as the topic, then identifies the particular person, time, place, reason, or other detail that completes it. It often corresponds to “the one who,” “the time when,” or “the reason why” in English.
How the pattern works
The の turns the preceding clause into a noun-like situation, and は makes that situation the topic. The phrase after it supplies the detail being identified. The particle is written は but pronounced わ, as with the ordinary topic marker.
What you can identify
The focused phrase can answer a question about a person, time, place, or reason.
このケーキを作ったのは姉です。
The person who made this cake was my older sister.
AnalyzeThe clause leaves the maker unidentified, and the final phrase supplies that person.
店が開くのは午前十時です。
The store opens at ten in the morning.
AnalyzeLiterally: The time when the store opens is ten in the morning.
私が鍵を見つけたのは玄関の前です。
The place where I found the key was in front of the entrance.
Analyze私が電車を降りたのは気分が悪くなったからです。
I got off the train because I started feeling sick.
AnalyzeLiterally: The reason I got off the train is that I started feeling sick.
Translate the focus naturally
English does not always need a matching “the one who” sentence. The important point is that the Japanese first presents the situation and then identifies one missing detail; the English translation can use whichever wording sounds natural.
Correcting an assumption
出発するのは金曜日ではなく、土曜日です。
Departure is on Saturday, not Friday.
AnalyzeThe focused phrase first rejects the assumed day and then gives the correct one.
More examples
私がこの町に引っ越したのは去年です。
I moved to this town last year.
AnalyzeLiterally: The time when I moved to this town was last year.
駅まで運転したのは山田さんです。
The person who drove to the station was Yamada.
Analyze二人が初めて会ったのはこのカフェです。
This café is where the two of them first met.
Analyze私が窓を開けたのは部屋が暑かったからです。
I opened the window because the room was hot.
AnalyzeLiterally: The reason I opened the window is that the room was hot.
私が探しているのは黒いかばんです。
What I am looking for is a black bag.
Analyze発表するのは私ではなく、森さんです。
Mori, not I, will give the presentation.
Analyze