Differences between なし and あらず?

Question

At some point in history, ない replaced *あらない as the negative of ある, at least in the Kantō dialect (Kansai seems to have あらへん; あらん is also apparently attested in some dialects).

When did this happen? That is, when did なし and its descendants replace あらず and its descendants? Were なし and あらず coexistent in the Heian period, or was one preferred over another? I see both used in later CJ texts, but it feels strange that there are two words with exactly the same meaning for such a common idea (not exist).

Currently, in polls etc you often see あり・なし as choices, rather than あり・あらず. Is this a Modern Japanese influence, or is this usage idiomatic (i.e. なし rather than あらず was seen as the obvious opposite of あり)

Additionally, does なし and あらず have different nuances?

Answer 1

あらず、is often used in 熟語、or old sayings (like 無きにしもあらず) probably made at least around 50 - 100 years ago.. but I don't know exactly when.

Nobody would say あらない・あらず in spoken or written language today. Although people can fully understand it, it's something you only read or hear people citing those old saying. It is not used in day-to-day life.

So, なし、simply means "there is not", while あらず meaning the same with the nuance that the sentence was composed / used long time ago. It also brings the nuance that the message conveyed has stood the test of time, and with a bit more authority, or properness. Modern people might intentionally use あらず to bring this atmosphere of some old saying even though the sentence might be composed quite recently.