In sentences that involve (Verb + べく) combinations, as in:


As for people close to me, (as much as possible) it's best to avoid them..


I went to the library (in order to study).

Are these phrases considered to form adverbs? E.g.

  1. (なるべく) is an adverbial phrase that modifies いい.
  2. (勉強すべく) is an adverbial phrase that modifies 行った.

If not, is there an official term which describes them better than 副詞?

  • 1
    Except なるべく, which is completely lexicalized, this construction has a formal or archaic tone to it.
    – aguijonazo
    Apr 6, 2023 at 3:56

1 Answer 1


The auxiliary べき is inflected like a Classical -i adjective. Or I guess, more historically accurately, as a Classical -ki adjective.

(Note: This was introduced to me using the adnominal -ki form. Other materials might start from the terminal / dictionary form ending in -shi instead.)

活用形【かつようけい】 Inflection Form
未然形【みぜんけい】 Irrealis / Incomplete ---
連用形【れんようけい】 Continuative / Adverbial べく
終止形【しゅうしけい】 Terminal / Predicative
(also "Dictionary Form")
連体形【れんたいけい】 Adnominal べき
已然形【いぜんけい】 Realis / Conditional べけれ
命令形【めいれいけい】 Imperative ---
  • Note: Many Japanese grammars include a mizenkei for adjectives, as this is the canonical conjugation for verbs for constructing the negative. However, for adjectives, the negative simply comes after the adverbial, and moreover it is clearly separable as you can insert a particle between the adverbial ~く and the following ない.

Since べく is clearly the adverbial conjugation, yes, such phrases are syntactically and grammatically adverbial.

PS: Can anyone help file a bug report for how the furigana are not working when included within a table?

  • The dictionary form of this word is べし, and I learned it inflects like a ku- adjective (ク活用). Is there any reason why you used the term ki-adjective and introduced this auxiliary with べき as the "default" form?
    – naruto
    Apr 6, 2023 at 3:27
  • 2
    @George Yes. 勉強すべし "You should study"; 勉強すべき本 "the book you should study"; 勉強すべく図書館に行った "went to the library in order to study".
    – naruto
    Apr 6, 2023 at 3:38
  • 1
    @naruto, I was simply coming from my experience with English-language instruction for Japanese: this was how this was introduced to me, with the adnominal. I'll add mention of the "dictionary form" to the table for clarity. Apr 6, 2023 at 17:06
  • 1
    @George, the conjugations above shifted over time into modern usage -- the adnominal came to be used for the terminal form as well (possibly due in part to older writing that uses the adnominal at the end of a sentence, as a specific kind of stylistic construction), pushing out the -し ending. Then there was also a sound shift so that the //k// in the -き and -く endings dropped out, leaving -い for the adnominal/terminal and -う for the adverbial. This -う adverbial persists in formal expressions like おめでとう (from adjective めでたい → めでたく → めでたう) and おはよう (from はやい), and in Kansai and other dialects. Apr 6, 2023 at 17:16
  • 1
    @George -- (cont'd) -- For reasons that I don't understand yet, the -き → -い shift took root in both Kansai and Kantō, but the -く → -う shift didn't persist in Kantō Japanese, with the older -く still hanging around for the adverbial. Main point: older Japanese has different adjective endings from the modern language, and a distinction between adnominal and terminal forms (-き for adnominal, -し for terminal). Apr 6, 2023 at 17:20

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .