The Overgeneralised Indicative after «باید»
An HSC candidate is correcting a classmate's sentence in a grammar drill. The original Odia sentence means «To pass the examination, I must study every day.» The classmate writes: «برای قبولی در امتحان، باید هر روز درس می‌خوانم.» The candidate says the sentence is correct because «می‌خوانم» shows a habitual action, and habit is exactly what the Odia sentence expresses. The teacher marks it wrong and writes only: «بعد از باید، فعل را دوباره نگاه کن.» The drill has four items, all with باید, and the classmate has used the indicative present in all four. The candidate has five minutes to explain the pattern, give the corrected sentence, and state one exception involving past obligation. The class has already learned the present stem and personal endings but has not yet practised negative subjunctive.
1. Correct the sentence and explain the grammatical trigger, not just the label.
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Correct sentence: «برای قبولی در امتحان، باید هر روز درس بخوانم.» «باید» expresses obligation and selects the subjunctive in the following verb when the obligation is present or future. The present subjunctive is بـ + present stem + personal ending; the present stem of خواندن is خوان, so the form is بخوانم. «می‌خوانم» is indicative and asserts habit or fact; it cannot carry the modal obligation after «باید» in this construction. The habit meaning is already carried by «هر روز», so the subjunctive does not lose habituality.
2. The classmate asks: «Can می ever appear after باید?» Give a precise answer with one example.
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Yes, but not in this present-obligation pattern. With a past obligation or reproach, «باید» can combine with a past continuous form: «باید می‌خواندم» - I should have been studying / I ought to have studied. The «می» belongs to the past continuous, not to a present indicative after «باید». So «باید می‌خوانم» is not acceptable for «I must study»; «باید بخوانم» is the correct present form.
3. How would you explain the negative version «I must not study» without producing «باید نمی‌خوانم»?
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Use نباید + subjunctive: «نباید بخوانم» or, more explicitly, «نباید درس بخوانم.» The negative of obligation is normally «نباید», not «باید» plus a negative indicative. «باید نخوانم» can occur in some contexts meaning «it is necessary that I not study», but it is marked and should not be the default. The ungrammatical form is «باید نمی‌خوانم»; «می» does not belong there.