What is ておく?
ておく is what you use when you do something now for a reason that matters later. It's about preparation, foresight, or deliberate intent. "I'll buy groceries (before the guests arrive)." "I studied (in advance for the test)." "Leave the window open (on purpose)."
The structure is て form + おく. The verb おく on its own means "to put/place," but as an auxiliary it carries the sense of doing something and leaving it in that state -- either as preparation or as a deliberate choice.
The Core Meanings
1. Doing something in advance / preparation
This is the most common use. You're taking action now because it will be needed or useful later:
- 明日のために勉強しておく。
I'll study in advance for tomorrow. - パーティーの前に部屋を掃除しておいた。
I cleaned the room (ahead of the party).
2. Leaving something as-is intentionally
Sometimes ておく means you did something and you're choosing to leave the result in place:
- エアコンをつけておいて。
Leave the AC on. - そのままにしておく。
I'll leave it as it is.
3. Doing something for now (temporary measure)
ておく can also signal that you're doing something as a stopgap, not a permanent solution:
- とりあえずメモしておく。
I'll jot it down for now.
Conjugation
おく is a u-verb, so it follows standard u-verb conjugation:
| Form | Example |
|---|---|
| Present (casual) | 買っておく |
| Present (polite) | 買っておきます |
| Past (casual) | 買っておいた |
| Past (polite) | 買っておきました |
| Negative | 買っておかない |
| Te-form | 買っておいて |
Casual Contraction: とく
In spoken Japanese, ておく contracts to とく. This is extremely common and not slangy at all -- you'll hear it in everyday conversation:
| Full Form | Contraction |
|---|---|
| 買っておく | 買っとく |
| 調べておく | 調べとく |
| 言っておいた | 言っといた |
| 予約しておいて | 予約しといて |
とく conjugates as a u-verb too: とく, といた, とかない, etc.
ておく vs てしまう
Both involve completing an action, but the feeling is very different:
- ておく -- deliberate, planned. You're doing it on purpose, with an eye to the future.
- てしまう -- complete, often accidental or regrettable. Something is done and you can't undo it.
Compare:
- 食べておいた。
I ate it (in advance / so it wouldn't go to waste). [Intentional] - 食べてしまった。
I ate it (all gone / shouldn't have). [Regret or completion]
Example Sentences
-
旅行の前にホテルを予約しておいた。 (ryokou no mae ni hoteru wo yoyaku shite oita.)
I booked a hotel before the trip. -
明日使うから、材料を買っておきます。 (ashita tsukau kara, zairyou wo katte okimasu.)
I'll buy the ingredients since we'll use them tomorrow. -
窓を開けておいてください。 (mado wo akete oite kudasai.)
Please leave the window open. -
会議の資料を準備しとくね。 (kaigi no shiryou wo junbi shitoku ne.)
I'll prepare the meeting materials (in advance), OK? -
電気をつけといて。 (denki wo tsuketoite.)
Leave the lights on. -
テスト前にこの文法を覚えておいたほうがいい。 (tesuto mae ni kono bunpou wo oboete oita hou ga ii.)
You should memorize this grammar before the test. -
先に言っておくけど、明日は忙しいよ。 (saki ni itte oku kedo, ashita wa isogashii yo.)
Just letting you know in advance, I'm busy tomorrow. -
パスポートをコピーしておきましょう。 (pasupooto wo kopii shite okimashou.)
Let's make a copy of the passport (just in case).