In short

Three ordinary verbs park themselves on the て-form and stop meaning what they used to: しまう (“finish it off” / “oh no, I’ve gone and …”), おく (“do it in advance, ready for later”) and みる (“do it and see how it turns out”). The main verb freezes in the て-form; the auxiliary at the end carries all the tense and politeness. Learn these three and a huge amount of everyday Japanese stops sounding like a guess.

The rule

A 補助動詞 hojo dōshi (“helping verb”) is a real verb that has been bleached of its literal meaning and attached to a て-form. Because it has stopped being literal, it is written in kana: しまう, おく, みる - never 仕舞う, 置く, 見る in this use. That kana spelling is the reader’s signal that the word is grammar, not vocabulary.

Step 1 - Build the て-form of the main verb (from lesson 13). It never changes again.

Step 2 - Attach the auxiliary and conjugate only the auxiliary: 読む yomu -> 読んで yonde -> 読んでしまいました yonde shimaimashita. Everything the sentence needs - past, negative, polite, request, たい - lands on the last element.

〜てしまう has two readings, and context picks one.

1. Completion - the action is carried through to the end, often faster or more thoroughly than expected. その本は読んでしまいました (Sono hon wa yonde shimaimashita) - “I’ve finished that book, all of it.” Words like 全部 zenbu (“all”) and もう mō (“already”) push this reading.
2. Regret / unintended irreversibility - it happened, it cannot be undone, and you are not happy about it. 忘れてしまいました (wasurete shimaimashita) - “I’ve gone and forgotten it.” 落としてしまいました (otoshite shimaimashita) - “I dropped it (and now it’s lost).”

The two readings are the same grammar seen from two angles: the action is done and closed. The most common form by far is the plain past 〜てしまった 〜te shimatta - it is the standard reaction to a small disaster.

〜ておく: do it now, for the sake of later. The pattern is V-て + おきます.

1. Preparation. You act in advance, because something is coming: 予約しておきます (yoyaku shite okimasu) - “I’ll book it (ahead of time).” 調べておいてください (shirabete oite kudasai) - “Please look it up beforehand.”
2. Leaving something as it is. The “preparation” is not touching it: そのままにしておく (sono mama ni shite oku) - “leave it as it is.” Here おく keeps a shade of its old meaning, “put/leave”.

〜てみる: do it and see. V-て + みます means you perform the action as an experiment, to find out what it is like: 食べてみます (tabete mimasu) - “I’ll try it (and see how it tastes)”. Very often it appears as 〜てみたい 〜te mitai (“I’d like to give it a go”): 行ってみたいです itte mitai desu.

〜てみる is not English “try to”. English “try” covers two different things, and Japanese splits them:

• “try doing something, to see what happens” -> 〜てみる. 納豆を食べてみました (Nattō o tabete mimashita) - “I gave nattō a go.”
• “try to do something, make an attempt that may fail” -> 〜（よ）うとする, built on the volitional and owned by lesson 38. 納豆を食べようとしました means “I attempted to eat nattō” - and implies you may not have managed it.

Stacking. Auxiliaries can pile up, but not in any order - each one takes the て-form of what is already there, and the meanings have to make sense in that sequence. 食べてみてください (tabete mite kudasai, “please try eating it”) is natural: try -> request. 買っておいてください (katte oite kudasai, “please buy it in advance”) is natural too. But ×読んでおいてしまう is odd - “finish off preparing to read” is not a thought anyone has. Whatever the stack, only the final verb conjugates.

Where these sit next to the state forms. Three te-form patterns are easy to confuse because English translates them all with “is …” or “have …”. They are not interchangeable: 〜ている and 〜てある describe a state, 〜ておく describes the act that creates it.

Not in this lesson: the directional pair 〜ていく／〜てくる (lesson 39) and the benefactive 〜てあげる／てくれる／てもらう are auxiliaries too, but each has its own lesson.

Forms & patterns

Building the three. The main verb’s て-form is fixed; the auxiliary is what you conjugate.

Conjugating the auxiliary. しまう and おく are Group I (五段); みる is Group II (一段).

Note that おく is a く-verb, so its て-form follows the いて rule: 〜ておいて 〜te oite, never ×〜ておって.

Contractions (casual speech - see lesson 44). The rule follows the voicing of the て-form: a て-form in て contracts with ち／と, one in で with じ／ど.

〜てみる has no contraction. Recognise the others, but keep the full forms in your own polite speech.

State versus preparation - the contrast to keep straight.

Examples

Common mistakes

• 読んでしまました。 (Yonde shimamashita.) -> 読んでしまいました。 (Yonde shimaimashita.) - しまう is a Group I う-verb, so the polite stem is しまい〜, exactly like 買う -> 買います. Dropping the い is the commonest spelling slip in this pattern.
• 飲んでちゃった。 (Nonde chatta.) -> 飲んじゃった。 (Nonjatta.) - the contraction follows the voicing already in the て-form. で-forms (the ぬ・ぶ・む・ぐ verbs) give じゃう／じゃった, never ちゃう／ちゃった.
• 映画を見て見ます。 (Eiga o mite mimasu.) -> 映画を見てみます。 (Eiga o mite mimasu.) - identical in sound, wrong on the page. The main verb keeps its kanji (見て), but the auxiliary is bleached and written in kana (みます). The same holds for しまう and おく.
• ホテルを予約しています。 (Hoteru o yoyaku shite imasu.) -> ホテルを予約しておきます。 (Hoteru o yoyaku shite okimasu.) - 〜ている reports a state or an action in progress; it cannot express “I’ll do it in advance so that it’s ready”. That job belongs to 〜ておく.
• 納豆を食べようとしました。 (Nattō o tabeyō to shimashita.) -> 納豆を食べてみました。 (Nattō o tabete mimashita.) - if you mean “I tried nattō (to see what it was like)”, use 〜てみる. 〜（よ）うとする means you attempted it, and hints that you failed.

Tips

• Think of 〜てしまった as “I’ve gone and …”. That English phrase carries both readings at once - completion and dismay - which is exactly the Japanese range. When you break, forget, drop, oversleep or eat the last one, this is the form a native speaker reaches for.
• 〜ておく is the travel-and-office verb. Any time you can say “beforehand”, “in advance” or “ready for later” in English, 〜ておく is probably the Japanese. Book it, check it, buy it, print it: 予約しておく, 確認しておく kakunin shite oku, 買っておく.
• Auxiliaries are written in kana, and that is a rule you can read backwards. If you see 見る, 置く or 仕舞う in kanji after a て-form, the writer means the literal verb - 本を置いて (hon o oite, “putting the book down”) is not 〜ておく at all.
• Only the last verb inflects. However long the chain gets - 買っておいてください, 食べてみてください - the て-forms in front are frozen. Beginners often try to make the main verb polite (×食べますてみます); politeness lives at the end of the sentence, and nowhere else.