auxiliary, ku-adjective (archaic)
Formal/literary auxiliary expressing strong obligation or expectation. In modern Japanese, べき is the more common equivalent. Used primarily in writing or set phrases.
See also: べき
Students must study hard.
auxiliary adjective, ku-adjective (archaic)
will surely; be bound to
Formal/literary auxiliary indicating strong certainty or inevitability. Often used in classical or highly formal contexts.
If you make an effort, you will surely succeed.
auxiliary, ku-adjective (archaic)
will do; shall
Formal/literary auxiliary indicating volition or intention. Equivalent to ～よう or ～つもり in modern Japanese.
I shall proceed along this path.
One should know oneself.
Promises should be kept.
べからず is the negative classical form meaning 'must not / shall not', the direct opposite of the obligation sense of べし.
Standard modern kana spelling for this classical auxiliary. The kanji form 可し is rare and archaic.
Rare kanji form; almost never used in modern Japanese. Included for recognition of classical texts.
Classical Japanese auxiliary verb. The exact derivation is uncertain, but it has been used since Old Japanese to express obligation, certainty, and volition.