Conjugational endings change in spoken Persian:

pastpresentcomment
1S-am-am
2S-i-i
3S--e«-ad» changes to «-e»
1P-im-im
2P-in-inthe same «-id» is also heard
3P-an'-an'the final «d» of «-and» drops but
the same «-and» is also heard

Look at the conjugation of «neveshtan» (to write):

Past simplePresent imperfectPresent subjunctive
1Sنوشتم
neveshtam
می‌نویسم
minevisam
بنویسم
benevisam
2Sنوشتی
neveshti
می‌نویسی
minevisi
بنویسی
benevisi
3Sنوشت
nevesht
می‌نویسه
minevise
بنویسه
benevise
1Pنوشتیم
neveshtim
می‌نویسیم
minevisim
بنویسیم
benevisim
2Pنوشتین
neveshtin
می‌نویسین
minevisin
بنویسین
benevisin
3Pنوشتن
neveshtan'
می‌نویسن
minevisan'
بنویسن
benevisan'

Narrative tenses

In narrative tenses, the past participle and the past endings go on a contraction. For example: «neveshte+am» becomes «nevesht'am». Please note that «neveshtam» (I wrote) and «nevesht'am» (I have written» are not pronounced identically. In «neveshtam» the stress falls on the syllable right before that of the ending (the penultimate): «ne.vesh.tam», whereas in «nevesht'am» the stress is on the last syllable: «ne.vesh.tam». The only form that remains distinct in writing is 3S as it does not take ending. See:

Past simplePast narrative
1Sنوشتم
neveshtam
نوشتم
nevesht'am
2Sنوشتی
neveshti
نوشتی
nevesht'i
3Sنوشت
nevesht
نوشته
neveshte
1Pنوشتیم
neveshtim
نوشتیم
nevesht'im
2Pنوشتین
neveshtin
نوشتین
nevesht'in
3Pنوشتن
neveshtan'
نوشتن
nevesht'an'

As you see, Persian alphabet does not have a character to denote contractions. Unfortunately, this causes past simple and past narrative appear alike in writing (but not in speech, as explained). Even native speakers occasionally make a mistake in telling them apart. For example, when writing down a recorded informal interview …

ضبط کار یا آلبوم تازه‌ای رو شروع کردی؟
Zabt-e kâr yâ âlbom-e tâze-i ro shoruø kardi?

… where شروع کردی (“shoruø kardi”) is in past narrative and must be written: شروع کرده‌ای (“shoruø kardei”).

In Persian's native script, there is no way to write past narrative correctly (in fact, contractions in general). But when writing in Latin script, contractions can be shown with apostrophe: shoruø kard'i

Although the difference can easily be detected from speech (from stress position) but it can also be detected from the “third person singular” form, which remains distinct and distinguishable. In order to decide whether شروع کردی is a narrative, you can simply consider the sentence in 3S form. For example, here it would be شروع کرده, which means the tense is past narrative. This tip can also be used for other narrative tenses. Example:

Rewriting it in 3S form, results in شنیده بوده and therefore, this tense is past precedent narrative and not past precedent:

Further reductions

Historically, there is a common phonemic reduction in the evolution of Persian: reduction of VCV to V (V = vowel; C = consonant). That is to say, whenever a word has a VCV pattern, it is disposed to be reduced to either V's. This reduction can occur in verb conjugations as well.

raftan /rav/
BeforeAfter
1Smiravammiram
2Smiravimiri
3Smiravadmirad —> mire
1Pmiravimmirim
2Pmiravidmirid —> mirin
3Pmiravandmirand —> miran'
goftan /gu/
BeforeAfter
1Smiguyammigam
2Smiguyimigi
3Smiguyadmigad —> mige
1Pmiguyimmigim
2Pmiguyidmigid —> migin
3Pmiguyandmigand —> migan'