I'm writing the documentation of a software package which has an optional property. In that context, which is more correct or more frequently used: non-optional or non optional?

Searching for the more frequently used form in google is difficult, because a non-optional search shows non optional results as well.

This is for writing software documentation that explains the usage of an optional property which some objects have.


There are similar constructions where it's not clear whether hyphenation is preferred or separate words, but this is definitely not one of them. A normal Google search for language use is problematic in many ways. In most cases it's better to use Google's n-gram viewer, which is a linguistic tool based on Google's corpus of scanned books and handles even capitalisation and punctuation correctly. (With the exception of commas, unfortunately.)

It has plenty of hits for "non-optional" and "nonoptional" but none for "non optional".

Based on this, I think we should think of non- as a prefix that just happens to be frequently written with a hyphen because it still feels foreign.

  • Thanks everybody for the answers, all of them are top-notch. It's hard to chose which one to accept. I'll do so with this one for pointing out Google's n-gram viewer as an authoritative source. Sep 9 '15 at 9:22

"Non" is a prefix that is either used with a hyphen (or other type of dash) or joined to the next word without a hyphen. It is not used as a stand-alone word. Whether you use a hyphen or not depends on the style. By default, British English includes the hyphen. Many American styles do mostly not include the hyphen. For instance, this style suggests to use hyphenation only to avoid doubling a letter (e.g. non-negotiable) and for cases where the prefix goes with a hyphenated compound.


Personally I would ditch that construction altogether in favor of something like:

Mandatory: required by law or rules; compulsory.

  • 3
    That's a good suggestion, thanks! However, I'm asking this because I'm writing the documentation of a software package which has an optional property, so maybe non-optional or non optional is clearer in this case. Which one would you use? Sep 9 '15 at 1:01
  • 2
    @RicardoSánchez-Sáez - I'd use optional and required in technical documentation. That follows the RFC guidelines ietf.org/rfc/rfc2119.txt which is what is used for internet standards documentation and influences most (good) technical documentation. Sep 9 '15 at 5:47
  • Thanks for linking the rfc! I think we'll switch to required after all. Sep 9 '15 at 9:34

This is a matter of style, so consult your style guide. The Chicago Manual of Style prefers words with prefixes, including "non" be closed, i.e., not hyphenated and no separating space. Thus "nonviolent." But there is an exception if letter combinations might be confusing. If you don't use a hyphen, the word at first glance might look to some like "no/no/ptional". The solution is "non-optional."

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