باید

Etymology
Originally the third-person singular present of the verb, hence etymologically "it is necessary". The original verb is now obsolete except in a few conjugations, of which is the most common and important.

The Middle Persian ancestor of this verb form was.

Usage notes

 * The negated means “must not” as a prohibition, and not “to not have to” as a lack of an obligation.  thus means “you must not go,” not “you don’t have to go.” To express “to not have to,” use expressions such as,.

Conjugation

 * See.