In Classical Japanese (correct me if I'm wrong; all my CJ was from Wikipedia and linguistic papers), the 已然形 could attach a lot of things: ど, ば, ども, etc. So I would be able to say 会へども話せず rather than 会うけれど話せない?
Anyways, where does the
ker- part come from in all these supplanted forms of the 已然形? Is there once some helping 四段 verb ける? If so, what would it mean?