Do I need to put a "-" between "non" and an adjective? As an example in physics we say "a non isolated photon", "non tight photon"... The context is very formal (paper publications and similar). Is there a general rule? Are there some differences between countries?


3 Answers 3


Yes, a two-word modifier (like this one) requires a hyphen, except that the commonly held convention is that adverbs ending in "ly" don't (like that one). See this table in the Chicago Manual of Style.

  • It is not to do with ending in "ly". e.g. "a fly-by-night transaction." Rather the rule is that one does not hyphenate adverb modifiers: "a hard won battle"
    – Robino
    Commented Aug 18, 2016 at 9:08
  • Hello, Monica. Nowadays, this would not be regarded as a good answer (whether right or wrong). Could you add some supporting evidence for your claim, please? Commented Aug 18, 2016 at 11:00
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    @Robino Whose rule? Wikipedia's rather good article on compound modifiers contains: 'It may be appropriate to distinguish between compound modifiers whose adverb has the suffix -ly, such as quickly and badly, and those whose adverb does not, such as well. The -ly suffix on an adverb allows readers to understand its lexical category (if not in the technical sense, then at least in the sense of the intended meaning), showing that it is intended to modify the adjective that it precedes and so not requiring hyphenation.... Commented Aug 18, 2016 at 11:03
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    Quickly and badly are unambiguously adverbs. Other adverbs (such as well) can commonly be used as adjectives; therefore these adverbs without the -ly suffix are accompanied by a hyphen. For example, one could speak of a well-known actress or a little-known actress.' Commented Aug 18, 2016 at 11:04
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    Except "non" is not an English word, it is a prefix of Latin origin. Which is why American style manuals will always ask you to merge it with the subsequent word, without a hyphen. British rules differ, and the "non-" construction is frequently found in the literature. In any case, an isolated "non" is definitely wrong, in any flavo[u]r of the English language. Commented Jan 11, 2019 at 13:50

As an addendum to Monica's fine answer, I'd like to add that there is a third possibility: fusing "non" with the word it precedes. A typical example would be "nonrelativistic", which seems to be Merriam-Webster's choice.

Similarly, one reads nonnegative, nonmagnetic, nonferrous, etc.

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    True, and this seems to be a case-by-case call. Some "non" words have entered the language (nonsense, for example), and in other cases dropping the hyphen seems to impede comprehension (nonisolated, from the OP). I don't know if there's a pattern. Commented May 25, 2011 at 0:52

I find many words in dictionaries have a definition (necessary: definition follows), but others do no (unnecessary: not necessary) as we see here I still have to look up the word necessary to find out what not necessary means. Using the word nonsense as another example I will show sense (has definitions) but nonsense (has definitions but they are not meanings held to the prefix NOT applying without fail. In this case it is easy for me to see that nonsense versus non-sense where nonsense has acquired a new meaning SEPARATE from the applied non(not) prefix meaning should only be.

So I myself, contrary to all I have read by so called 'Usage Panels' of experts who list such reasonings as 60% agree or only 39% find this acceptable or blah... from that I know this: "If you do not have an absolute rule and answer, then there isn't one, it is simply one of anyone's preference".

That said, I then choose to put a hyphen between any word I choose... when I am using the implied meaning of the prefix (whether it is non(not) or otherwise) because at least I choose to make it known and not up to interpretation by any reader... what my intent is, and this is whenever I question the meanings that exist by definition that the reader may choose from. If there are too many interpretative choices in a non-hyphened usage to my liking, I will include the hyphen.

Note: I can't recall at the moment, hyphenating suffixes because they generally do not change meanings or include new definitions, but rather they usually only provide characterization of an object or its action as applies to tense, inflection, mood, etc, but if used, use it the same way as a prefix.

  • I broke this up into paragraphs to make it easier to read. Hope you don't mind.
    – MrHen
    Commented Jul 5, 2014 at 15:39

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