What is the difference between supposedly and supposably? Both are real words but seem to have confusingly similar definitions.
Supposably: Capable of being supposed : conceivable
Supposedly: According to what is generally assumed or believed
Supposably does mean "it is possible to suppose", as opposed to the very different meaning of "supposedly"!
Supposably is quite rare in actual use; I believe it's more an inkhorn term than one actually found in the wild, so to speak. Thus, I fear that when you encounter it you are probably really encountering somebody who meant to say "supposedly".
I have never heard of the word "supposably" before. Sure enough it's in the dictionary; maybe it's an obsolete word. I suppose (!) it is very rare.
"Supposedly" is usually used to mean, "most people think this is true but I think it is questionable or clearly false". Like, "Today I read an article in a supposedly unbiased newspaper." The sentence implies that the article was in fact biased. Or: "Supposedly, at 8:00 am the employees are all at their desks working." Maybe they should be or they're expected to be, but they really aren't.
Quite frankly, I would never use "supposably." It is, however, certainly present in the American vernacular. As I am a lawyer "supposedly" is most synonymous to "based upon an allegation" and I have used it in that context. "Supposably," were I perchance to ever use it (doubtful/in a creative writing context maybe) would be used in the context more akin to "supposably winters in San Francisco feel warmer than summers." Personally, I shouldn't use either word. Neither is (is there a thread on "both are not," and "Neither is?") as descriptive as another word would be. For example: alleged or assumed. Just sayin....