Thanks for that .
Hmm -none of the thesauruses (thesauri?) had therefore =then or babble =rave .
I can't think of a sentence where you can substitute then for therefore.
I think babbling means more talking incoherently than raving.
I can safely say that I've never heard of The Raven.
In my dreams if this had been a crossword competiton. I might have been in with a shout until that very last clue -how cruel that would have been!