The Iranian languages are spoken in an area that ranges from eastern Turkey in the west to Central asia in the east. The westernmost Iranian language is Zazaki in Turkey and the easternmost language is the Pamir language Sarikoli spoken in the Sinkiang province of the People's Republic of China.
The Iranian languages form a top-level constituent of the Indo-European language family. Iranian is closely related to Indo-Aryan. Ssome scholars merge Iranian and Indo-Aryan because of the close relationship into one subbranch of the Indo-European language family, called Indo-Iranian.
The history of the Iranian languages is divided into three stages: Old Iranian (- 200 BCE), 2) Middle Iranian (200 BCE - aftermath of the Islamic conquest of the Sasanian Empirein the 7th century CE) and 3) New Iranian (9th century CE -). Old Iranian languages are Old Persian and Avestan, Middle Iranian Languages are Middle Persian (also called Pahlawi), Parthian, Sogdian, Khwarazmian, Bactrian,and Saka.
Iranian languages are subdivided by linguists traditionally into West Iranian and East Iranian.
The New West Iranian traces back historically to the Old Iranian languages Old Persian and Median and the Middle Iranian languages Middle Persian and Parthian. New West Iranian is subdivided into two groups, in (a) the Southwest Iranian languages, which are descendants of dialects of Old and Middle Persian or genetically related languages, which are not attested, and in (b) the Northwest Iranian languages, which are descendants of Median and Parthian or genetically related languages, which are not attested.
The grouping inside the New West Iranian languages does not rely on the present geographical location of the single languages but on their historical filiation. Balochi, for instance, is spoken in the extreme southeast of the Iranian-speaking area. However, it shows a close genetical affinity to the Middle Iranian language Partian, which was spoken in the northeast, and therefore is classified.
East Iranian is subdivided into a northern and southern subgroup, as well. There is no Old Iranian language, that can be unequivocally classified as East Iranian. However, some scholars refer to Avestan as East Iranian language. In the Middle Iranian stage, there are Northeast Iranian languages attested, but no Southeast Iranian languages. Members of the southeastern group do not show up before the New Iranian stage. Northeastern Middle Iranian languages are Sogdian, Khwarazmian, Bactrian,and Saka. The two northeastern lanaguages of the New Iranian stage are: Ossete and Yaghnobi and the southeastern branch of New Iranian is represented by Pashto and the Pamir languages.
Persian and Pashto are the only New Iranian languages with an ancient literary tradition. New Persian literature is as old as the 10th century CE and Pashto is a literary language since the 16th century CE.
Most New Iranian literary languages are written with modified Arabic letters, e. g. Persian and Pashto, some are written with Roman letters, e g. Zazaki, some are written with both, e. g. Kurdish. Iranian languages in the former Soviet Union are written with Cyrillic based letters.
Iranian has lost the complex nominal inflection of the Old Iranian languages (up to eight cases, three numbers, htree genders) already in the Middle Iranian stage. Many New Iranian languages have preserved two cases (singular, oblique) and two genders (masculine, feminine), but various languages have abandoned case inflection and gender distinction.
The complexity of the Old Iranian verb inflection has been lost in the Middle Iranian stage. New Iranian verb inflection is usually based on three stems: present stem, past stem and perfect stem. The present stem derives historically from the Old Iranian present stem, the past stem goes back to the Old Iranian past partiple and the perfect stem is the past stem augmented by a suffix.
Many New Iranian languages have a split ergative construction. The historic roots of this ergative construction trace back to the Old Iranian linguistic stage, when the old synthetic perfect was replaced by an analytic construction with passive value. In Old Persian this replacement is attested by the renowned 'mana kartam'-construction ('by me it was done'). The subject of a transitive verb in the new perfect takes the genitive-dative case, whereas in Sanskrit the agent in that construction is marked by the instrumental case. The oblique case, which marks the agent of transitive verbs in the past tenses of Middle Iranian and New Iranian languages, stems from the Old Iranian genitive-dative case. In Hindi the subject of a transitive verb in the past tense is marked by a special agentive or ergative particle that has instrumental etymology. Most New East Iranian languages have ergative past tenses. The remarkable exception is Ossetic, which is spoken in the Caucasus area that is famous for the multitude of ergative languages spoken there. Among the West Iranian languages are many languages, which have lost the ergative structure of the past tenses. For instance New Persian, the Iranian language with the greatest number of speakers, is a purely accusative language. However languages like Kurdish, Zazaki, Gorani and other smaller languages have retained the ergative construction.
The order of constituents in Iranian languages is usually SOV.
Due to Islamisation most Iranian languages have a considerable amount of Arabic loanwords in their word stock. Iranian languages spoken in the former Soviet Union commonly feature Russian loan words. Loanwords from western languages such as French and English are also quite wide-spread among Iranian languages.