Proto-Indo-Iranian language in the context of "Proto-Indo-Aryan language"

Avestan (/əˈvɛstən/ ə-VESS-tən) is the liturgical language of Zoroastrianism. It belongs to the Iranian branch of the Indo-European language family and was originally spoken during the Avestan period (c. 1500 – 400 BCE) by the Iranians living in eastern Greater Iran as evidenced from names in Avestan geography.

After Avestan became extinct, its religious texts were transmitted orally, then collected and put into writing during the Sasanian period (c. 400 – 500 CE). The extant material falls into two groups: Old Avestan (c. 1500 – 900 BCE) and Younger Avestan (c. 900 – 400 BCE). The immediate ancestor of Old Avestan was the Proto-Iranian language, a sister language to the Proto-Indo-Aryan language, with both having developed from the earlier Proto-Indo-Iranian language. As such, Old Avestan is quite close in both grammar and lexicon to Vedic Sanskrit, the oldest preserved Indo-Aryan language.

Vedic Sanskrit, also simply referred as the Vedic language, is the earliest attested form of the Sanskrit and Prakrit languages: members of the Indo-Aryan subgroup of the Indo-European language family. It is attested in the Vedas and related literature compiled over the period of the mid-2nd to mid-1st millennium BCE. It is orally preserved, predating the advent of writing by several centuries.

Extensive ancient literature in the Vedic Sanskrit language has survived into the modern era, and this has been a major source of information for reconstructing Proto-Indo-European and Proto-Indo-Iranian history.

The Gathas (/ˈɡɑːtəz, -tɑːz/) are five hymns in the Avestan language from the Zoroastrian oral tradition of the Avesta. The oldest surviving text fragment dates from 1323 CE, but they are believed by scholars to have been composed before 1000 BCE and passed down orally for centuries. They are traditionally believed to have been composed by the prophet Zarathushtra (Zoroaster) himself. They form the core of the Zoroastrian liturgy (the Yasna). They are arranged in five different modes or metres.

The Avestan term gāθā (𐬔𐬁𐬚𐬁 "hymn", but also "mode, metre") is cognate with Sanskrit gāthā (गाथा), both from the Proto-Indo-Iranian word *gaHtʰáH, from the root *gaH- "to sing".

Proto-Iranian or Proto-Iranic is the reconstructed proto-language of the Iranian languages branch of Indo-European language family and thus the ancestor of the Iranian languages such as Persian, Pashto, Sogdian, Zazaki, Ossetian, Mazandarani, Kurdish, Talysh and others. Its speakers, the hypothetical Proto-Iranians, are assumed to have lived in the 2nd millennium BC and are usually connected with the Andronovo archaeological horizon (see Indo-Iranians).

Proto-Iranian was a satem language descended from the Proto-Indo-Iranian language, which in turn, came from the Proto-Indo-European language. It was likely removed less than a millennium from the Avestan language, and less than two millennia from Proto-Indo-European.

As the Proto-Indo-European language (PIE) broke up, its sound system diverged as well, as evidenced in various sound laws associated with the daughter Indo-European languages.Especially notable is the palatalization that produced the satem languages, along with the associated ruki sound law. Other notable changes include:

• Grimm's law and Verner's law in Proto-Germanic
• an independent change similar to Grimm's law in Armenian, dubbed the Armenian Consonant Shift
• Adjarian's law in Proto-Armenian
• loss of prevocalic *p- in Proto-Celtic
• Brugmann's law in Proto-Indo-Iranian
• Winter's law and Hirt's law in Balto-Slavic
• merging of voiced and breathy-voiced stops, and /a/ and /o/, in various "northern" languages
• Sturtevant's law
• Cowgill's laws of Germanic and Greek
• Osthoff's law
• Slavic first, second and third ("progressive") palatalization

Bartholomae's law in Indo-Iranian, and Sievers's law in Proto-Germanic and (to some extent) various other branches, may or may not have been common Indo-European features. A number of innovations, both phonological and morphological, represent areal features common to the Italic and Celtic languages; among them the development of labiovelars to labial consonants in some Italic and Celtic branches, producing "p-Celtic" and "q-Celtic" languages (likewise "p-Italic" and "q-Italic", although these terms are less used). Another grouping with many shared areal innovations comprises Greek, Indo-Iranian, and Armenian; among its common phonological innovations are Grassmann's law in Greek and Indo-Iranian, and weakening of pre-vocalic /s/ to /h/ in Greek, Iranian and Armenian.