Q: Where did “supposably” come from? It’s not in my dictionary and I find it annoying to hear. Am I wrong? Is it acceptable usage?
A: Most people assume that “supposably” is a mangled version of “supposedly.” And it almost always is, in our experience.
But there’s more to the story.
Both “supposedly” and “supposably” are legitimate adverbs. Although they were used rather loosely in the past, they now have separate meanings.
Current dictionaries will tell you that “supposedly” is the adverbial counterpart of “supposed,” an adjective that can mean presumed, believed, understood, or imagined.
The less common “supposably” is the adverbial counterpart of “supposable,” an adjective that means conceivable—that is, capable of being supposed.
We’ll invent a couple of examples to illustrate the difference in accepted modern usage:
(1) “Supposedly he didn’t know the gun was loaded.” Here the adverb means “it is supposed (presumed, imagined) that he….” Note the skeptical overtone, because “supposedly” often implies an element of doubt.
(2) “Supposably he didn’t know the gun was loaded.” Here the adverb means “it is conceivable that he….” No skepticism is implied. Instead, the speaker seems to suggest, “Let us imagine that he ….”
We’ve described these adverbs as they’re defined today in standard dictionaries, which assign them separate meanings. But as you’ve probably noticed, people who use “supposably” seldom mean it in the current dictionary sense. They almost always mean “supposedly.”
That’s reason enough to stay away from “supposably.” In the dictionary sense of the word, alternatives like “conceivably” do the job better, and no one will assume you made a mistake.
But as we said, there’s more to the story.
A century or more ago, “supposably” was seen more often in respectable writing. And its meaning varied a lot, as we found in Google searches.
In this passage from Henry James’s novel The Tragic Muse (1890), “supposably” means something like “presumably”:
“If … Percy had an heir (others, moreover, would supposably come), Nick should have to regard himself as still more moneyless than before.”
Here it is again in William Dean Howells’s novel A Foregone Conclusion (1886): “But I’m not supposably the kind of priest you mean, and I don’t think just such a priest supposable.” The character seems to be saying, “You cannot suppose me to be … (etc.).”
And in this passage from Mark Twain’s novel Pudd’nhead Wilson (1894), “supposably” is used in the sense of “supposedly”:
“Over in the vacant lots was Jasper … sitting on a wheelbarrow in the pelting sun—at work, supposably, whereas he was in fact only preparing for it by taking an hour’s rest before beginning.”
Twain used “supposably” in a similar way in his essay “Is Shakespeare Dead?” (1909). This passage comes after several paragraphs describing what historians “suppose” (the skeptical Twain uses quotation marks) about Shakespeare’s childhood:
“If he began to slaughter calves, and poach deer, and rollick around, and learn English, at the earliest likely moment—say at thirteen, when he was supposably wrenched from that school where he was supposably storing up Latin for future literary use—he had his youthful hands full, and much more than full.”
It can be difficult to tell what a writer of the past meant by “supposably.” This ambiguous example is from a paper by Karl P. Harrington, published in the Classical Journal in 1920:
“So far, indeed, as the recurrence of literary motifs is concerned, the apparent identity of ideas supposably far removed from each other in character and setting tempts the scoffer to give credence to Mark Twain’s famous remark, that, after all, there are but two extant jokes.”
In short, “supposably” has a history of ambiguity. And the Oxford English Dictionary still accepts this mixed usage without comment.
The OED currently says that “supposably” means “as may be supposed; imaginably; presumably; supposedly.” But it notes that the word is now used “chiefly” in the United States.
The OED’s first citation for “supposably” is from 1739 (the older “supposedly” dates from 1597). And in the earlier quotations, the apparent meaning of “supposably” is “as may be supposed.”
But in contemporary usage, “supposably” isn’t seen much in good writing, except when used for effect.
For example, the OED’s most recent citation is this bit of dialogue from Sue Grafton’s novel L Is for Lawless (1995):
“ ‘Did they call the police?’ ‘Uhn-hun, and they’re on their way. Supposably,’ she added with disdain.”
We took a look at Grafton’s novel. The second speaker, Babe, consistently uses uneducated English, like “the window was broke, all this glass laying on the steps.” So Grafton no doubt chose “supposably” as an example of poor usage.
As the OED says, “supposably” is now used chiefly in the US. With its history of ambiguity, perhaps Americans would be wise to drop it.
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