Upanishads
Chronology

Scholars are uncertain about when the Upanishads were composed. The chronology of the early Upanishads is difficult to resolve, states philosopher and Sanskritist Stephen Phillips, because all opinions rest on scanty evidence and analysis of archaism, style and repetitions across texts, and are driven by assumptions about likely evolution of ideas, and presumptions about which philosophy might have influenced which other Indian philosophies. Indologist Patrick Olivelle says that "in spite of claims made by some, in reality, any dating of these documents that attempts a precision closer than a few centuries is as stable as a house of cards".

Some scholars have tried to analyse similarities between Hindu Upanishads and Buddhist literature to establish chronology for the Upanishads. Precise dates are impossible, and most scholars give only broad ranges encompassing various centuries. Gavin Flood states that "the Upanisads are not a homogeneous group of texts. Even the older texts were composed over a wide expanse of time from about 600 to 300 BCE." Stephen Phillips places the early or "principal" Upanishads in the 800 to 300 BCE range.

Patrick Olivelle, a Sanskrit Philologist and Indologist, gives the following chronology for the early Upanishads, also called the Principal Upanishads:

Meanwhile, the Indologist Johannes Bronkhorst argues for a later date for the Upanishads than has generally been accepted. Bronkhorst places even the oldest of the Upanishads, such as the Brhadaranyaka as possibly still being composed at "a date close to Katyayana and Patañjali " (i.e., c. 2nd century BCE).

The later Upanishads, numbering about 95, also called minor Upanishads, are dated from the late 1st-millennium BCE to mid 2nd-millennium CE. Gavin Flood dates many of the twenty Yoga Upanishads to be probably from the 100 BCE to 300 CE period. Patrick Olivelle and other scholars date seven of the twenty Sannyasa Upanishads to likely have been complete sometime between the last centuries of the 1st-millennium BCE to 300 CE. About half of the Sannyasa Upanishads were likely composed in 14th- to 15th-century CE.
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