There are two classes of infinitives in Persian: verbs ending in –dan, as in[tag resources infinitives_01] دیدن [/tag]didan ‘to see,’ [tag resources infinitives_02] خوردن [/tag]xordan ‘to eat’; and verbs ending in –tan, as in[tag resources infinitives_03] گفتن [/tag]goftan ‘to say,’[tag resources infinitives_04] نشستن [/tag]nešastan ‘to sit.’

In the case of verbs ending in -dan, the infinitival suffix may follow:

• a vowel:[tag resources infinitives_05] دادن [/tag]dādan ‘to give,’[tag resources infinitives_06] شنیدن[/tag]šanidan ‘to hear,’[tag resources infinitives_07] گشودن [/tag] gošudan ‘to open’
• the flap (/r/):[tag resources infinitives_08] خوردن [/tag]xordan ‘to eat,’ [tag resources infinitives_09] مردن [/tag]mordan ‘to die,’[tag resources infinitives_10] کردن [/tag]kardan ‘to do’
• the nasal /n/:[tag resources infinitives_11] کندن [/tag]kandan ‘to cut off, dig,’[tag resources infinitives_12] خواندن [/tag]xāndan ‘to read’

The causative invariably has an [-ān-] ending before its infinitival suffix [-dan]: [tag resources infinitives_13] نشاندن [/tag]nešāndan ‘to seat, set,’ خوراندن xorāndan ‘feed,’ [tag resources infinitives_14] خواباندن [/tag]xābāndan ‘to put to sleep,’ [tag resources infinitives_15] سوزاندن [/tag]suzāndan ‘to burn.’

In the case of verbs ending in –tan, the infinitival suffix follows a consonant: گفتن goftan ‘to say,’ نشستن nešastan ‘to sit,’ [tag resources infinitives_16] گذشتن [/tag]gozaštan ‘to pass (by),’[tag resources infinitives_17] سوختن [/tag]suxtan ‘to burn.’

The infinitive in Persian is normally equated with the English infinitive, but it is more like the English gerund, that is, a verb in -ing when it does not represent a progressive form as in “Reading is good”: خواندن کار خوبی است xāndan kār-e xubi ast “Reading is good.” Therefore, in Persian an infinitive also functions as a gerund.

In Persian the only verb with an initial ī (ای) is the verb[tag resources infinitives_18] ایستادن [/tag]intransitive verb ‘to stand (up); stop.’

The only verb in Persian with a single sound for the present stem is the verb[tag resources infinitives_19] آمدن [/tag]āmadan ‘to come,’ with the present stem آ -ā-; as in, mi ā-yam ‘I come’ (with an euphionic [-y-] intervening between the stem and the personal suffix -am).