A long-time subscriber to our Good Word series and e-friend, Jackie Strauss of Philadelphia, recently wrote the following:
“I’m curious about the word arguably. People seem to use it to mean that what they’re saying is unarguable, that the fact they’re espousing is iron-clad and exactly correct in their opinion, e.g. “She is arguably the best tennis player the world has ever known.” Are they daring you to argue with that statement or saying it cannot be argued with?”
I think you heard people simply misusing the word. Arguably is what is known as a “sentence adverb”, an adverb that modifies the whole sentence. Sentence adverbs usually may be paraphrased as “It is arguable that (sentence)”. Further examples: Apparently (it is apparent that), he missed the boat. Surprisingly (it is surprising that), he arrived early.
Hopefully is little off key because it doesn’t paraphrase this way; the paraphrase of this word is something like “It is (to be) hoped”. But all languages are strewn with exceptions to every rule of grammar. The same problem faces thankfully. However, this rule applies nicely to all the other sentence adverbs, like basically, certainly, clearly, conceivably, curiously, etc.
Hopefully, this has helped.