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
学生はよく勉強すべし。
Students must study hard.
約束は守るべし。
Promises should be kept.
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.
努力すれば成功するべし。
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.
我、この道を進むべし。
I shall proceed along this path.
Classical Japanese auxiliary verb. The exact derivation is uncertain, but it has been used since Old Japanese to express obligation, certainty, and volition.