The exceptions to the modifier rule are common compound modifiers, and a few combinations of particular word types (e.g. adjective + adjective).
Common compound modifiers
Compound modifiers that have become well established will often lose the hyphen. Depending on the types of words used in the phrase, these are left open or set solid.
Leave the compound open for common forms of:
- adjective + noun
- noun + noun
Set the compound solid for common forms of:
- noun + participle
- noun + gerund
- words beginning with the prefixes on- or off-
- adverbs
Combinations of particular word types
Four combinations of word types do not follow the modifier rule.
Hyphenate the compound, whether it occurs before or after the noun, for:
- adjective + adjective
a bitter-sweet story the story is bitter-sweet
a red-hot surface the surface is red-hot
- noun + adjective
disease-free animals the animals were disease-free
HIV-positive man the man was HIV-positive
Do not use a hyphen, whether the compound occurs before or after the noun, for:
- adverb ending in -ly + participle or adjective
a heavily edited script the script was heavily edited
naturally occurring chemicals chemicals that are naturally occurring
- adverb + adjective
a rather boring book the book was rather boring
a very popular author the author is very popular