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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?

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2 Answers

up vote 13 down vote accepted

Yes, a two-word modifier (like this one) requires a hyphen, except that the commonly held convention is that words ending in "ly" don't (like that one).

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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. –  Monica Cellio May 25 '11 at 0:52
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