～ておく or ～とく for preparation (conjugation and nuance)

Question

A few quick questions regarding ～ておく and the casual form ～とく

Firstly, when changing from ～ておく to the more casual ～とく　I'm assuming the verb is first conjugated to the ～て　form then the ～て is dropped and replaced with とく and it can then be conjugated following the godan conjugation pattern as in the examples below.

I.e.

勉強して　→　勉強しておく　→　勉強しとく

～とく conjugates as godan such that 勉強しときます and　勉強しときました. In the case of verbs that have a ～で ending do they conjugate as どく？

I.e.

読んで　→　読んでおく　→　読んどく

～どく　also conjugates as godan such that 読んどきます and 読んどきました

Is my understanding correct here?

Also, are there any nuances that make it outright different from ～つもりです in terms of preparing for something?　Is it simply that one of the sentences below feels more natural than the other?

For example

明日試験があるので今晩勉強しておきます
vs
明日試験があるので今晩勉強するつもりです

Answer 1

Yes, all your assumptions about about the conjugations are correct.

And far as comparing it to つもり, つもり simply means "intention (to do something)". It doesn't directly have anything to do with preparation or doing something beforehand. That it carries this mean in your example is incidental. With your 勉強しておく sentence, the preparation is explicit; with the 勉強するつもり sentence, the preparation is implicit. But in general, using つもり is not for preparatory situations.

• 昨晩雪がたくさん降ったので、週末にスキーに行くつもりです　→　It snowed a lot last night, so I intend to go skiing this weekend.

Answer 2

When you contract te oku to t'oku, you're still conjugating oku, so the normal rules apply. The only reason this might not be clear is that kana prevents us from dividing t'oku into t' and oku.

Subsidiary verbs following ～て are grammaticalized, and people tend to contract grammatical words. So naturally, there are a number of contractions of ～て with subsidiary verbs you'll need to recognize, and each one needs to be memorized individually. Some of them only appear in certain dialects (or appear more often in specific dialects):

　

uncontracted	contracted	uncontracted	contracted
〜ている	〜てる	-te iru	-te'ru
〜ていく	〜てく	-te iku	-te'ku
〜ておく	〜とく	-te oku	-t'oku
〜ておる	〜とる	-te oru	-t'oru
〜てしまう	〜ちまう 〜ちゃう	-te simau	-t'imau -t'yau
〜ていらっしゃる	〜てらっしゃる	-te irassyaru	-te'rassyaru
〜てある	〜たる	-te aru	-t'aru
〜てやる	〜たる	-te yaru	-t'aru
〜てあげる	〜たげる	-te ageru	-t'ageru

All of these have corresponding voiced versions when they contract with ～て's voiced allomorph ～で, which in the case of ～ちまう・～ちゃう gives us ～じまう・～じゃう.

Of course, there are more contractions I haven't listed here, and I couldn't begin to describe the range of dialectal variation out there, but I think these are the main ones I've run into as a learner of Japanese.

Answer 3

It might help to think about what's going on with 「ておく」 and 「とく」 in romaji.

" 勉強 shiteoku "

The we just drop the 'e' ('cause we're cool kids)...

" 勉強 shitoku "

The same kind of thing happens all the time with 「い」"i"

「何食べている？」 becomes 「何たべてる？」 (just drop the 「い」)
"Nani tabeteiru?" becomes "Nani tabeteru?" (Just drop the 'i')

This can seem more confusing when it's written in kana because kana generally represent a unique combination of consonant + vowel.

I have seen romaji used this way in junior high school and elementary school to explain the finer points of Japanese verb conjugation to students.