Ask Language Log: why is "whether or not" more frequent?
Ton van der Wouden asks:
The Google Ngram viewer shows a tenfold increase in the frequency of the string "whether or not". Can the readers of language log think of any explanation for this growth? Can it perhaps be traced back to some prescriptive source? Is it perhaps accompanied by a comparable decrease of the frequency of the variant with postposed "or not", as in "whether you like it or not" — a string that is too long a search term for the Ngram viewer.