Where it sits
Real, old and correct in its own sense; criticised when used to mean supposedly.
What it doesn't mean
It's a real word with its own history going back to at least 1696. Merriam-Webster says so directly: 'supposably is a word'.
Not originally. Supposably means 'as may be conceived or imagined'. Supposedly usually means 'allegedly' — according to what people say.
What it really means
Supposably has a reputation as a mistake, and it's half-earned.
The word itself is genuine. As checked in October 2026, Merriam-Webster lists it and answers the question in an article headed with the reassurance that both words are real. Dictionary.com defines it as "as may be assumed, imagined, or supposed". It comes from supposable, an adjective Merriam-Webster dates to 1627, and Merriam-Webster quotes it in print from 1696.
So what's the problem? Two adjectives, supposable ("capable of being supposed, conceivable") and supposed, overlap in meaning. Their adverbs, supposably and supposedly, sound almost the same in quick speech. Over time, many speakers started using supposably to mean what supposedly means: allegedly, according to what people say.
That modern use is the one that gets criticised. In older writing, Merriam-Webster notes, supposably usually has its own distinct meaning, "capable of being conceived of". Many people today intend it to mean something much closer to supposedly, and that, in the dictionary's words, bothers some people.
Merriam-Webster's conclusion is a fair summary of the verdict: supposably is a word, with a meaning distinct from most uses of supposedly, but most people who reach for it would be better served by supposedly.
A quick test: if you could replace it with allegedly or apparently, write supposedly. If you mean conceivably, supposably is correct, though "conceivably" may be clearer.
Where it comes from
English, 1627 (M-W) — capable of being supposed; conceivable
English — adverb ending
Supposably comes from supposable, just as supposedly comes from supposed. The two adjectives overlap in meaning, which is how their adverbs got tangled.
- 1627
The first known use of the adjective supposable, in Merriam-Webster's entry.
- 1696
Supposably in print, in Samuel Hill's A Debate on the Justice and Piety of the Present Constitution — quoted by Merriam-Webster.
- Today
Merriam-Webster: many modern users intend it to mean 'allegedly', a sense that 'bothers some people'.
In real life
- "It's supposedly the best curry house in town," he said — not supposably, which would mean it could conceivably be.
- The shortcut was supposedly quicker, though by the third roundabout nobody believed it.
- A supposably rational plan, her dad said, was not the same thing as a sensible one.
Questions
Q01Is supposably a real word?
Yes. Merriam-Webster lists it and has a whole article on it; Dictionary.com defines it as 'as may be assumed, imagined, or supposed'. Its earliest example in Merriam-Webster's article is from 1696.
Q02What's the difference between supposably and supposedly?
Supposedly means 'allegedly' or 'according to what people say': 'he was supposedly at home'. Supposably means 'conceivably' or 'as may be imagined'. They sound alike, and that's the source of the mix-up.
Q03Is it wrong to say supposably?
Only if you mean supposedly. Merriam-Webster's verdict is that supposably is a word with its own meaning, but most people who use it today would be better served by supposedly.
Sources
- 'Supposably' vs. 'Supposedly' — Merriam-Webster.
- supposable / supposably — Merriam-Webster.
- supposably — Dictionary.com.