--For your information--
There exists a regulation on the combination; some grammatical tips are needed to understand it. It doesn't apply to works such as novels published in books. Here I roughly explain its rules as to adjectives and verbs.
Maybe it's better to know exceptions first. Some exceptions from 明らむ to 巧みだ are listed on the reference page:
http://www.mext.go.jp/b_menu/hakusho/nc/k19730618001/k1...Adjectives
- Each adjective whose end-form is "...shii": the part "..." is written in Kanji. e.g. 美しい [utsukushii], 楽しかっ-た[tanoshikat-ta].
- Other adjectives: the stem (i.e. part which doesn't change by forms) is written in Kanji. e.g. 快い [
kokoroyoi], 快かっ-た [
kokoroyokat-ta].
Verbs
- a. Each verb whose end-form needs two letters in Kana: the first letter is written in Kanji. e.g. 見る [miru], 得-ない [e-nai], 得る [eru / uru], 来-た [ki-ta], 来る [kuru].
- b. Each verb whose end-form is "...suru": the part "..." is written in Kanji. e.g. 安心し-た [anshinshi-ta], 理解する [rikaisuru].
- c. Each verb whose six forms end with vowel
a,
i,
u,
u,
e,
e in this order: the stem is written in Kanji. e.g. 見逃さ-ない [minoga
sa-nai], 見逃し-ます [minoga
shi-masu], 見逃す [minoga
su], 見逃す 時 [minoga
su toki], 見逃せ-ば [minoga
se-ba], 見逃せ [minoga
se].
- d. Each of other verbs whose end-form ends with iru
or a consonant & iru: the part before the ending is written in Kanji. e.g. 悔いる [kuiru], 恥じ-た [haji-ta].
- e. Each of other verbs whose end-form ends with eru
or a consonant & eru: the part before the ending is written in Kanji. e.g. 負ける [makeru], 認め-た [mitome-ta].
- f. Regardless of b. through e., if a verb Y's stem includes a noun X / a verb X / an adjective X's stem, then the combination in Y depends on X. e.g. 春めく [harumeku], 生まれる [umareru] (stem 生ま includes v.生む [umu]), 逃がす [nigasu] (stem 逃が includes v.逃げる [nigeru]), 悲しむ [kanashimu] (stem 悲し is also stem of adj.悲しい [kanashii]).
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