ク活用

Japanese

From く (-ku, the 未然形 (mizenkei, “incomplete form”) and 連用形 (ren'yōkei, “stem form”) of adjectival suffix し (-shi)) +‎ 活用 (katsuyō, “declension, inflection”).

ク活用(かつよう) • (ku katsuyō) ^{←くくわつよう (kukwatuyou)^?}

(Classical Japanese grammar) an adjective inflection class for some classical adjectives ending in -shi:

Archaic	未然形 Irrealis	連用形 Adverbial	終止形 Conclusive	連体形 Attributive	已然形 Realis	命令形 Imperative
清し (kiyoshi, “clear”)	清く (kiyoku) 清から (kiyokara)	清く (kiyoku) 清かり (kiyokari)	清し (kiyoshi)	清き (ki₁yo₁ki₁ → kiyoki) 清かる (kiyokaru)	清けれ (ki₁yo₁ke₁re → kiyokere)	清かれ (kiyokare)
高し (takashi, “high, tall”)	高く (takaku) 高から (takakara)	高く (takaku) 高かり (takakari)	高し (takashi)	高き (takaki₁ → takaki) 高かる (takakaru)	高けれ (takake₁re → takakere)	高かれ (takakare)
良し (yoshi, “good”)	良く (yoku) 良から (yokara)	良く (yoku) 良かり (yokari)	良し (yoshi)	良き (yo₂ki₁ → yoki) 良かる (yokaru)	良けれ (yo₂ke₁re → yokere)	良かれ (yokare)

The subscripts in the table above indicate differences in vowel class that were already being lost in Old Japanese. It remains unclear what those different vowel classes may have meant. See the Syllables section in the Wikipedia article on Old Japanese for more details.

Adjectives in this class are often related to objective properties or status, as opposed to adjectives of the シク活用 (shiku katsuyō) class.
Adjectives in this class are superseded by the い (-i) inflection in modern Japanese:
清(きよ)し (kiyoshi) → 清(きよ)き (kiyoki) → 清(きよ)い (kiyoi)

高(たか)し (takashi) → 高(たか)き (takaki)→ 高(たか)い (takai)

良(よ)し (yoshi) → 良(よ)き (yoki) → 良(よ)い (yoi)

^ Matsumura, Akira, editor (2006), 大辞林 [Daijirin] (in Japanese), Third edition, Tokyo: Sanseidō, →ISBN