べし

Etymology
From. First attested in the  of 712.

Suffix

 * 1)  must, shall

Usage notes

 * This word is morphologically a clitic. It is classified as in traditional Japanese grammar.  Syntactically, it is essentially a verb suffix, attaching only to the terminal or predicative form of the verb rather than to any of the other conjugation stems.
 * This inflects very similarly to Classical adjectives.
 * The verb typically takes the classical terminal form ', rather than the modern terminal form ', when used with :  ("should do").
 * However, there is a minority that uses.

Inflection

 * The modern conjugation of べし is a combination of its classical conjugation and the conjugation of べき +.