When we say,

It is not fair.


It is unfair.

I'm not sure enough to say whether both of the sentences have the same meaning or not though superficially, there is no difference between them but if we say,

Something is not possible.


Something is impossible.

then there is really an observable difference in my first language. Hence, the question - is there a difference between the preceding two sentences in English?

  • 1
    An extensive corpus search might tell us that they were used in different contexts. Or it might not. Commented Oct 29, 2012 at 8:22

4 Answers 4


To me the only difference is style: one word (unfair) versus two words (not fair). The same for impossible and not possible: both mean cannot be done for some reason or other.

  • 1
    In response to "We would never say It's not possible": Such claims are presumptuous because they imply an omniscience that only a novelist has. Predicting what native speakers will say is based on probability & statistics. I never know what I'll say until I say it. Context decides. I might not even say it in English: I might say "Muri da yo!(Japanese for "Impossible!") to my Dutch friend who's fluent in Japanese & English. If I want to say it without implying that you're stupid, I'd say "That's not possible". If I want to be dismissive, I might say "Impossible!"
    – user21497
    Commented Oct 29, 2012 at 8:56
  • In your next comment, you say that the two ways of denying something are not equal. I agree that this is sometimes true. Style differences can, but don't always, express speaker attitude differences. Some speakers & writers don't care about or, perhaps, understand the flux or feculence of word choice, word order, or style. Some do. What I said, of course, was just about me & my idiolect, not a claim about what other native speakers think. No trouble. You always ask good questions. I always try to give you a good, honest answer without being arrogant. I don't know it all.
    – user21497
    Commented Oct 29, 2012 at 9:13
  • 1
    @Tiny In my mother tongue, German, I would say both It's not possible and It's impossible when someone would tell me the sun is going to rise on the wrong side. Though, I believe there's a slight difference, based on the way I would stress the words: That's impossible (, you stupid idiot) vs That is not possible (and you know that). Not sure about English anyway.
    – Em1
    Commented Oct 29, 2012 at 9:27
  • @Em1: I think it's generally the same in English, but I'm sure only about what I think.
    – user21497
    Commented Oct 29, 2012 at 9:29
  • @Tiny: You're a very bright young fellow (I'm 69). It's delightful to read your questions and comments. Your English is outstanding for a 12-year-old, native speaker or not. Your desire to learn is refreshing in a world filled with people of all ages who want only to be entertained. We all make claims & judgments: it's okay. That's not an accusation of wrongdoing. You claim there's a difference in your 3 other languages between "not possible" & "impossible". That may be true. I don't know. Other native English speakers may feel the same about that in English. I say sometimes, not always.
    – user21497
    Commented Oct 29, 2012 at 11:44

I don't think there's any difference of meaning between unfair and not fair, or impossible and not possible; but there are all sorts of other reasons why you might choose one over the other. A few examples:

  • Discourse Context — If someone says to you, “This proposition is not very probable”, you would very likely mirror his construction and say “Not probable? It's not possible!” But if he had said “This proposition is improbable” you would respond "“Improbable? It's impossible!

  • Register & Rhetoric — If you have seen the movie The Princess Bride you may recall that Vizzini is given to saying “Inconceivable!”, and is eventually rebuked by Fezzik that “I do not think it means what you think it means.” Vizzini's use, of course, is ordinary colloquial hyperbole, and “Impossible!” is often used the same way. Accordingly, in conversation, when you mean impossible literally you may prefer to say not possible, so that you will not be understood to mean merely very unlikely.

  • Prosodic Context — The im- in impossible and un- in unfair are unstressed syllables, and don't take stress as readily as not. Small children (in my experience) always shriek “It's not fair!” rather than “It's unfair!” when someone else gets something they want—somehow the spondee is just more indignant than the iamb. In print, similarly, you might use not possible if you feel that italicizing the first syllable of impossible (impossible) doesn't emphasize the negative adequately—or if, like me, you've never figured out how to emphasize just a segment of a string in these postings.

  • RE. your last line: you have to use single asterisks instead of underscores to italicise parts of words: *im*possible --> impossible.
    – TripeHound
    Commented Aug 22, 2017 at 7:43

I'm not native english and my answer is not based on any source but only feeling. But I feel like impossible is more inherently cannot be possible by itself objectively. While not possible involve environmental condition

When I said "I think it's impossible" I means that thing cannot be done or I don't know any condition to let it could be done

When I said "I think it's not possible" I means that thing actually has probability or condition to let it possible but there was none or very little of those in the situation

  • 1
    This is an important distinction that hasn't been mentioned. "not possible" usually means "not possible at this moment" but not necessarily "never has and never will be possible", which is closer to "impossible". Examples: It's impossible for pigs to fly. It is not possible to change flights without incurring a fee
    – AlexR
    Commented Aug 4, 2022 at 15:51

When a word such as possible is negated by 'not', it simply relays the fact of what is not possible. However, when a new and separate word is formed by adding the prefix, it strengthens the word and increases the intensity of what is being relayed.

For example, if someone asked to use a car but were told that it was not possible, that would be one thing. But, if they were told that it was impossible to use the car, that would be another. The first answer leaves room for speculation. Perhaps a tire was flat, the driver wasn't trusted or it had already been promised to someone else. For whatever the reason, it was not possible.

The second answer gives no wiggle room. Regardless of any reason, that car is not going to be used. It is impossible.

  • I think you're implying what I'm thinking, which is that "not possible" can be modified by words such as "currently", whereas this is much less likely to happen with "impossible".
    – AndyT
    Commented Aug 22, 2017 at 10:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.