Although they appear to have the same meaning, I somehow feel "unnecessary" has a little bit of negative sense attached to it; "not necessary", however, has neutral feeling. For example,

"It was unnecessary." - It was not required to do anyways and you have made it little worse (speaker does not have a positive opinion of the listener).
"It was not necessary." - It was not required, but I don't mind anyways.

Can anyone please confirm whether my line of thinking is correct or not? If not, are they absolutely replaceable, with no difference in nuance at all?


"unnecessary" means "not needed", sometimes with a hint of "and not wanted"

"not necessary" means "not required"

Some Examples:

"Eating every day is not necessary" - Factual. You can still survive if you don't.

"Eating every day is unnecessary" - This would sound strange, since while it is not necessary, it is normal to do so.

"Rotating your car tires every week is not necessary" - Doesn't really hurt to do it but it's not needed.

"Rotating your car tires every week is unnecessary" - You really don't need to do this.


Oftentimes, there are differences, of varying magnitudes, in meaning between "unnecessary" and "not necessary". In some of these instances "unnecessary" can have a 'negative' undertone. For instance in "It was unnecessary." vs "It was not necessary." , "unnecessary" sounds slightly negative (in the sense that not only was it not required but it was also not wanted).

In other instances the difference is so slight that it might only be regional or not immediately distinguishable. In such cases it might be preferable to use other constructions over take the risk of the nuance being missed.

In other cases, such as "he can remember a lot of unnecessary details" / "he can remember a lot of not necessary details" only one version fits (due to reasons not necessarily related).

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    So it does have a little negative meaning after all? – Steel May 8 '14 at 7:42
  • So as I said, speaker doesn't have a fully "positive opinion" when he uses 'unnecessary'. In other words, it has a little negative nuance. – Steel May 8 '14 at 7:45
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    @Steel probably because we prefer to use opposites than negatives in such constructions: "He can sing a lot of not easy songs" - "He can sing a lot of difficult songs" - if you want a grammatical reason this has the potential of being a good question in itself. An equivalent version which might sound long-winded but less strange: "He can remember a lot of details that are not necessary to remember". In this case I don't see any difference from "He can remember a lot of details that are unnecessary to remember". In this context there is no difference between "not required" and "not needed" – msam May 8 '14 at 8:08
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    perhaps the reason "difficult songs" is preferred over "not easy songs" is that we want to emphasize the type of song - its "difficult"; not easy might not imply difficult. Similarly, in "unnecessary details", I feel we want to stress on the type of details by mentioning it's a little odd and strange thing by saying "unnecessary". In that way, I still think it retains its "little negative" sense. Note, the overall sentence is no way negative. – Steel May 8 '14 at 9:09
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    @Steel difficult vs not easy is another topic. The difference between unnecessary and not necessary is not always of the same magnitude. In some instances the nuance is very slight and might be regional. Where it's not as clear cut it might be preferable to use other constructions over take the risk of the nuance being missed. I would say that often there is a difference, with "unnecessary" being 'negative', other times one of them doesn't really fit ("he can remember a lot of not necessary details"), and other times the difference is so slight that it might not be immediately distinguishable. – msam May 8 '14 at 9:42

Not absolutely replaceable.

This is an unnecessary question

This is a not necessary question

You would need to slightly reword the second version for it to make sense, but generally these alternatives do appear to be interchangeable in many situations.

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    Can you clarify a bit more? I still have no idea how to distinguish them and know when to use which of them. – Steel May 8 '14 at 7:28
  • @Steel Honestly, I don't think I could. They can be used to mean exactly the same thing, any concept of being more negative than the other is a personal thing, it's only grammar that makes them not absolutely replaceable. – Frank May 8 '14 at 7:57

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