باید

Originally the third-person singular present of the verb بایستن (bâyestan, “to be necessary”), hence etymologically "it is necessary". The original verb is now obsolete except in a few conjugations, of which باید (bâyad, “should; must; have to”) is the most common and important.

The Middle Persian ancestor of this verb form was Middle Persian [Book Pahlavi needed] (ʾp̄ʾyt' /⁠abāyēd⁠/, “it is necessary, fitting; must”).[1]

بایَد • (bâyad)

1. (defective) Expresses an obligation or confident conjecture, equivalent to English must, have to, should, ought, etc.

   باید برود ― bâyad beravad ― he/she must go

   آن باید علی باشد ― ân bâyad 'ali bâšad ― that must be Ali

   باید رفت ― bâyad raft ― one must go [impersonal]

   باید رفته باشد ― bâyad rafte bâšad ― he/she should have gone [but it is not clear if he/she did]; or, he/she must have gone [a conjecture about a past event]

   باید می‌رفت ― bâyad mi-raft ― he/she had to go [and did go]; or, he/she should have gone [but did not go]

   • c. 1010, Abū’l-Qāsim Firdawsī, Shāhnāma:

     از آغاز باید که دانی درست
     سر مایهٔ گوهران از نخست
     که یزدان ز ناچیز چیز آفرید

     az âğâz bâyad ki dânî durust
     sar mâya-yi gawharân az naxust
     ki yazdân zi nâčîz čîz âfarîd

     From the start, you ought to know well
     The source of the essences from the beginning
     That God created a something from nothing.

     (Classical Persian transliteration)

   • 2009, شادمهر عقیلی (lyrics and music), “تقدیر”:

     باید تورو پیدا کنم

     bâyad to ro peydâ konam

     I have to find you

• The negated نباید (na-bâyad) means “must not” as a prohibition, and not “to not have to” as a lack of an obligation. نباید بروی (na-bâyad beravi) thus means “you must not go,” not “you don’t have to go.” To express “to not have to,” use expressions such as مجبور نبودن (majbur na-budan, “to not be obliged”), لازم نیست (lâzem nist, “it’s not necessary”).

• See بایستن (bâyestan).