Negation with نیست

01

The Forms

• ⁧⁧نیستَم⁩⁩ (nistamnistamnystm) - I am not
• ⁧⁧نیستی⁩⁩ (nistinistinysty) - you are not
• ⁧⁧نیست⁩⁩ (nistnistnyst) - he is not, she is not, it is not
• ⁧⁧نیستیم⁩⁩ (nistimnistimnystym) - we are not
• ⁧⁧نیستید⁩⁩ (nistidnistidnystyd) - you are not
• ⁧⁧نیستَند⁩⁩ (nistandnistandnystnd) - they are not

The stem is ⁧⁧نیست⁩⁩ (nistnistnyst) throughout, with the ordinary personal endings after it, and nothing at all in the third person singular.

• ⁧مَن مَریض نیستَم.⁩

  man mariḍ nistamman mariz nistammn mryḍ nystm

  I am not ill.

• ⁧او مُعَلِّم نیست.⁩

  u moʿallem nistu mo'allem nistav mʿllm nyst

  She is not a teacher.

• ⁧آن‌ها زیبا نیستَند.⁩

  ân-hâ zibâ nistandân-hâ zibâ nistandan-ha zyba nystnd

  They are not beautiful.

02

Also 'There Is Not'

Just as ⁧⁧هَست⁩⁩ (hasthasthst) means "there is", ⁧⁧نیست⁩⁩ (nistnistnyst) covers "there is not" - the same word doing both jobs.

• ⁧مُشکِلی نیست.⁩

  moškeli nistmoshkeli nistmškly nyst

  There is no problem.

• ⁧کاری نیست کِه نَتَوانَد اَنجام دَهَد.⁩

  kâri nist ke natavânad anjâm dahadkâri nist ke natavânad anjâm dahadkary nyst k ntvand anjam dhd

  There is nothing it cannot do.

That first sentence is worth memorising on its own: it is the everyday Persian for "no problem", "never mind", "it is fine".

03

Away From the Present

In the past and the subjunctive, "to be" negates the ordinary way, with the prefix ⁧نَ⁩ (na-) on the regular stem - ⁧⁧نَبود⁩⁩ (nabudnabudnbvd) for "was not" and ⁧⁧نَباش⁩⁩ (nabâšnabâshnbaš) for the subjunctive and the negative command.

• ⁧غَمگین نَباش.⁩

  ġamgin nabâšghamgin nabâshġmgyn nbaš

  Do not be sad.

• ⁧مَن غَمگین نیستَم.⁩

  man ġamgin nistamman ghamgin nistammn ġmgyn nystm

  I am not sad.

Those two lines sit side by side in a single exchange, and they show the split neatly: the command uses the prefix, the statement uses ⁧⁧نیست⁩⁩ (nistnistnyst).