What are the Old, Middle, and New stages of Indo-Aryan languages?

Linguists generally categorize the Indo-Aryan languages into three major historical stages. These divisions are linguistic in nature and reflect the chronological order in which the stages appeared, with later stages coexisting with rather than entirely replacing earlier ones.1

Old Indo-Aryan

This stage is collectively referred to as Sanskrit. The most archaic form is found in the Vedas, sacred texts dating to approximately 1500 BCE. This period includes distinct linguistic states, such as Vedic Sanskrit and later Classical Sanskrit, the latter of which was famously described by the grammarian Pāṇini around the 5th–6th century BCE.1

Middle Indo-Aryan

This stage encompasses the dialects found in inscriptions from the 3rd century BCE to the 4th century CE, as well as various literary languages. These languages are generally grouped under the term Prākrit, though this classification typically excludes Apabhraṃśa dialects, which represent the latest phase of Middle Indo-Aryan development.1

New Indo-Aryan

This stage comprises the wide variety of modern languages currently in use, such as Hindi, Bengali, Punjabi, and Marathi. These languages continue many of the phonological and structural trends that began during the Middle Indo-Aryan period, such as the reduction of noun cases and the simplification of vowel sequences.21