7. General hyphenation guide

Hyphens are what make the difference between a man-eating alligator and a man eating alligator.

Generally, the Chicago Manual of Style recommends that you should hyphenate compound phrases to avoid misdirecting the reader. When it doubt, they say, look it up in the dictionary. The goal of hyphens is to improve clarity on the relationships between words in a compound phrase. If there is a possibility the reader may be confused, it is best to use the hyphen and apply it consistently to a given phrase throughout the paper.

Examples of how hyphens can change the meaning of a phrase:

  • All inclusive classrooms are to be commended. (all classrooms that are inclusive)
  • All-inclusive classrooms are to be commended. (classrooms that are all-inclusive)
  • He submitted nine page reports that morning. (nine reports of one page)
  • He submitted nine-page reports that morning. (more than one report of nine pages)

When there is no possibility of ambiguity, there is no reason to use the hyphen unless it is standard usage, such as well-known, ill-humoured, long-term. Words that might be misread because the merged form already exists and has a distinct meaning should also gain a hyphen, such as re-form (form anew instead of reform) or re-pair (pair again instead of repair).

If the result is awkward, it is best to reword a sentence with too many hyphens.


  • The study covered a wide age-distance-metallicity-density parameter space.
  • The study covered a wide parameter space of ages, distances, metallicities, and densities.

Note: Two-word phrases with an adverb ending in ly are not hyphenated.

Examples: highly paid person, rapidly rotating planet.

Note: Compounds that use comparatives and superlatives with a participle (verb) have no hyphen.


  • fast-rotating galaxy; faster rotating galaxy; fastest rotating galaxy.
  • far-reaching findings; farther reaching findings; farthest reaching findings.

However, with compounds that use comparatives and superlatives with a noun, there is a hyphen:


  • high-mass star; higher-mass star (but: even higher mass star); highest-mass star.
  • high-resolution screen; higher-resolution screen; highest-resolution screen.
  • A high-mass star typically burns hydrogen faster than its lower-mass counterpart.

Hyphens in word-forming prefixes
Both UK and US conventions use merged and hyphenated word forms. The US spelling tends to merge common prefixes (e.g., multi, over, non) in compound nouns or adjectives, whereas the UK spelling is more likely to hyphenate.


  • We used a non relational database.
  • We used a nonrelational database (US convention)
  • We used a non-relational database (UK convention)

General note: The Chicago Manual of Style reports that with frequent use, both open and hyphenated compounds tend to become closed (as in the case of on-line to online; broad-band or broad band to broadband) and that is either reflected in the dictionary or should be expected to be reflected in an upcoming edition. This is why you may seem some discrepancy among spelling and hyphenation among various papers written by scientists from all over the world.

Here are some more points on when and how to use hyphens from the American Psychological Association: https://apastyle.apa.org/learn/faqs/when-use-hyphen