Are there any differences between 〜けらず and 〜ざりけり? Are they interchangeable?


Was ~ざりけり used in place of 〜けらず, for example in **知りけらず** , to indicate the
past tense in the negative form? Did **知らざりけり** exist?




〜ざりけり certainly existed and was very widely used. This definition includes a
couple of examples:

[https://kobun.weblio.jp/content/ざりけり](https://kobun.weblio.jp/content/%E3%81%96%E3%82%8A%E3%81%91%E3%82%8A)

I believe that 〜けらず was actually far less common than 〜ざりけり, at least from the
Heian period on, and the entry for けり in 大辞林 seems to confirm this – in fact,
it suggests that 〜けらず disappeared entirely. (The main definition indicates
that けり has no 未然形, so there would be nothing to attach 〜ず to; a note at the
end of the definition clarifies that 未然形「けら」は、「けらず」「けらく」の形で上代にのみ用いられる and
cites an example from 万葉集.) Also note that 〜ざりけり can and often does have an
exclamatory nuance. I'm not sure 〜けらず, on its own, conveys quite the same
feeling.

